Donald Trump said on Sunday that U.S. forces would start blockading maritime traffic to Iranian ports, escalating tensions after negotiations failed to produce an agreement to end the conflict, putting a fragile two-week ceasefire at risk.

US Central Command said the blockade would take effect at 10 a.m. ET (1400 GMT) and would apply to all vessels entering or leaving Iranian ports across the Arabian Gulf and the Gulf of Oman. It added that freedom of navigation through Hormuz to non-Iranian destinations would not be impeded.

Shipping data showed several vessels adjusting routes in response. The Malta-flagged very large crude carrier Agios Fanourios I reversed course after attempting to enter the Gulf and is now anchored near the Gulf of Oman.

Other tankers, including the Pakistan-flagged Shalamar and Khairpur, continued operations, heading toward the United Arab Emirates and Kuwait respectively to load cargo.

The Liberia-flagged VLCC Mombasa B also transited the strait earlier on Sunday and is currently ballasting in the Gulf, according to vessel tracking data.Iran’s Islamic Revolutionary Guard Corps warned that any military vessels approaching the strait would be considered a violation of the ceasefire and would face a “decisive” response.

Despite rising tensions, shipping data showed that three fully laden supertankers passed through the strait on Saturday, appearing to be among the first vessels to exit the Gulf since the ceasefire agreement was reached last week.

The Liberia-flagged Very Large Crude Carrier (VLCC) Serifos and China-flagged VLCCs Cospearl Lake and He Rong Hai transited via a designated passage that bypasses Iran’s Larak Island, according to data from LSEG.

Each vessel has the capacity to carry around 2 million barrels of oil.The Strait of Hormuz, through which about one-fifth of global oil and liquefied natural gas supplies pass, had been effectively blocked by Iran since the outbreak of conflict in late February, contributing to supply disruptions and a sharp rise in oil prices.

Serifos, chartered by Thailand’s state energy firm PTT, is carrying crude loaded from Saudi Arabia and the United Arab Emirates and is expected to arrive at Malaysia’s Malacca port on April 21, according to LSEG and Kpler data. It is among several vessels for which Malaysia had sought clearance from Iran to transit the strait, sources said.

Cospearl Lake, carrying Iraqi crude, is scheduled to reach Zhoushan port in eastern China on May 1, while the discharge destination for He Rong Hai, which is transporting Saudi oil, remains unclear. Both vessels are chartered by Unipec, the trading arm of Chinese energy major Sinopec.

Shipping data also showed that hundreds of tankers remain stranded in the Gulf awaiting passage during the limited ceasefire window, underscoring continued constraints on maritime traffic.At the same time, three empty tankers Mombasa B, Agios Fanourios I and Shalamar were navigating the strait to enter the Gulf and load crude.

One of them signaled plans to load Basrah oil in Iraq for delivery to Vietnam.Industry sources and companies involved did not immediately respond to requests for comment.

The partial resumption of tanker movement highlights the critical role of the Strait of Hormuz in global energy flows and the sensitivity of oil markets to geopolitical developments in the region.

Shipowners are seeking urgent clarification on the terms of a newly declared ceasefire between Iran and the United States that could reopen the Strait of Hormuz, as more than 800 vessels remain stranded following weeks of disruption to one of the world’s most critical energy corridors.

The partial shutdown of the strait, triggered by escalating conflict after US and Israeli strikes, has severely constrained maritime traffic through the narrow passage that connects the Arabian Gulf to global markets. Iran subsequently tightened its control over the waterway, leading to a near-total halt in shipping activity as security risks mounted.

Shipowners and operators have kept vessels anchored on both sides of the strait amid repeated attacks and the absence of guarantees for crew safety. The disruption has left a significant portion of the global tanker fleet immobilized, intensifying concerns over energy supply chains and freight logistics.

A ceasefire agreement announced shortly before a deadline set by Donald Trump has raised expectations of a temporary reopening. However, conflicting statements from Washington and Tehran have left critical operational details unresolved.

Iranian authorities have indicated that safe passage will be permitted for a period of two weeks, coordinated with their armed forces and subject to what they described as “technical restrictions.” In contrast, Trump characterized the agreement as enabling a “full, immediate, and safe opening” of the waterway. It remains unclear whether both sides have agreed on transit conditions, including any fees or procedural requirements imposed by Tehran.

The lack of clarity has prompted a cautious response across the shipping industry. The Japan Shipowners’ Association said it would first verify the terms of the agreement before advising its members on resuming operations. Industry participants broadly indicated that vessels would not begin moving until security assurances are substantiated.

Even under favorable conditions, analysts say restoring normal traffic flows will take time. In typical circumstances, approximately 135 ships transit the Strait of Hormuz each day, but volumes have fallen sharply during the crisis. Restarting operations involves coordination among shipowners, insurers, port authorities, and naval forces, all of whom must reassess risk levels before authorizing movement.

Jennifer Parker, an assistant professor at the Defense and Security Institute at the University of Western Australia, said the process cannot be immediate. She noted that stakeholders require evidence of sustained de-escalation rather than a temporary pause in hostilities before committing vessels and crews to transit.

Data from Kpler indicates that energy shipments account for a large share of the stranded fleet. Currently, 426 crude oil and refined fuel tankers are waiting in Gulf waters, along with 34 liquefied petroleum gas carriers and 19 liquefied natural gas vessels. Additional ships carrying dry bulk commodities and containerized cargo are also affected, reflecting the impact on multiple sectors of global trade.

The الأزمة has also created significant humanitarian concerns for maritime workers. According to the International Maritime Organization, around 20,000 civilian sailors are stranded aboard vessels in the region, including support and service ships. The agency has warned of mounting challenges related to supply shortages, fatigue, and psychological stress among crews who have been unable to disembark or proceed with their voyages.

For shipowners, the immediate priority remains clarity on operational protocols under the ceasefire framework. Questions persist over navigation corridors, coordination mechanisms with Iranian forces, insurance coverage, and liability in the event of renewed hostilities.

The Strait of Hormuz handles a substantial share of global oil shipments, making its accessibility central to energy market stability. Any prolonged disruption has direct implications for supply flows and price volatility, amplifying the importance of a clear and enforceable agreement.

While the ceasefire has introduced a potential pathway to easing the crisis, the absence of detailed, mutually verified terms continues to delay decision-making across the shipping industry, leaving hundreds of vessels and thousands of seafarers in a state of prolonged uncertainty.

The bottleneck includes 12 very large gas carriers and 50 very large crude carriers, with only six ships transiting the strait between Tuesday and Wednesday, far below the typical daily average of around 120 vessels in peacetime, data from maritime analytics firm Kpler showed.

Limited movement has been permitted through a tightly controlled corridor near Iran’s Larak Island, with access largely restricted to vessels linked to Iran or countries maintaining favorable relations with Tehran. Lloyd’s List estimates that at least 48 ships have passed through the route since last week under such arrangements.

Iran imposed the blockade following strikes by the United States and Israel on Feb. 28, effectively constraining a waterway that normally handles about one-fifth of global oil and gas shipments. Shipowners granted passage have reportedly faced fees of up to $2 million per transit, although Tehran has indicated that vessels from allied nations may be exempt.

Malaysian authorities said tankers operated by companies including Petronas, Sapura Energy and MISC were awaiting clearance, with Iran assuring Kuala Lumpur that fees would be waived due to bilateral ties. Officials cautioned that heavy congestion could delay passage regardless of exemptions.

China said at least three of its vessels had recently transited the strait following coordination with relevant parties. Ship-tracking data indicated that two container ships exited the Gulf on a subsequent attempt while sailing in close formation and at increased speed, in what analysts described as the first such movement by non-Iranian container vessels since the escalation began.

A small number of other ships have also managed to leave, including a Greek-operated tanker carrying Saudi crude to India and several Indian-flagged liquefied petroleum gas carriers transporting essential cargo.

Shipping sources said some crews have adopted risk mitigation measures such as nighttime navigation or disabling tracking systems to reduce exposure to threats including mines, missiles and drones.Despite limited transits, exports from major Gulf producers such as Saudi Arabia and Qatar remain largely suspended, with hundreds of vessels and an estimated 20,000 seafarers still awaiting clearance in and around the Gulf.

A Pakistani oil vessel reached Karachi after successfully transiting the strait, while another shipment arrived via an alternative route. Officials said further deliveries could follow in the coming weeks.The disruption has intensified diplomatic efforts to reopen the waterway.

Britain is preparing to host talks involving around 35 countries to address maritime security, while China and Pakistan have jointly called for a ceasefire and urged all sides to ensure safe passage for commercial shipping.U.S.

President Donald Trump reiterated on Wednesday that Iran must lift the blockade, warning of potential military action if it fails to comply.