The Tripoli Criminal Court convicted the four defendants in absentia, handing down prison terms ranging from 12 to 22 years, according to a statement published by the attorney general’s office on Facebook. The office did not disclose the identities of those convicted.

Prosecutors said the group was involved in smuggling undocumented migrants from the western coastal city of Zuwara, one of Libya’s main departure points for migrants attempting to reach Europe across the Mediterranean.

Authorities said the gang also abducted migrants and extorted ransom payments from their families, sending relatives videos showing victims being tortured in order to force payment.

Libya has become a major transit route for migrants and asylum seekers fleeing war, persecution and poverty in Africa and the Middle East since the 2011 NATO-backed uprising that toppled longtime leader Muammar Gaddafi and plunged the country into prolonged instability.

Migrants often travel through dangerous desert crossings before attempting sea journeys to Europe in overcrowded and unsafe boats operated by smuggling networks.Two weeks ago, at least 17 bodies believed to be migrants were recovered from the shores of Zuwara by a local medical service center, highlighting the continuing risks faced by those attempting the crossing.

Separately, Libya’s Public Prosecutor’s Office on Monday ordered the arrest of another criminal group accused of sending migrants from the eastern city of Tobruk across the Mediterranean on an unsafe and dilapidated vessel that later capsized.

Authorities said the incident resulted in the deaths of 38 migrants from Sudan, Egypt and Ethiopia.International scrutiny over Libya’s treatment of migrants has intensified in recent years.

In November, several countries including the United Kingdom, Spain, Norway and Sierra Leone urged Libya during a United Nations meeting in Geneva to close detention centers where rights groups say migrants and refugees have been tortured, abused and in some cases killed.