FILE PHOTO: Fatou Bensouda, Prosecutor of the International Criminal Court (ICC) poses for pictures at The Hague, Netherlands October 26, 2016. REUTERS/Michael Kooren

UNITED NATIONS (Reuters) - The International Criminal Court (ICC) prosecutor expressed alarm on Monday at the inhumane detention of thousands of vulnerable migrants in Libya and said she was examining whether an investigation could be opened into crimes against them.

Libya is the main gateway for migrants attempting to reach Europe by sea. The United Nations migration agency said more than 1,000 migrants have been reported dead or missing in the Mediterranean this year, while an unknown number perish in the desert.

According to the International Organization for Migration, 20,000 migrants are held by criminal gangs in irregular detention centers in Libya and growing numbers of migrants are traded in what they call slave markets before being held for ransom, forced labor or sexual exploitation.

ICC prosecutor Fatou Bensouda told the United Nations Security Council that her office was collecting and analyzing information “related to serious and widespread crimes allegedly committed against migrants attempting to transit through Libya.”

“I take this opportunity before the council to declare that my office is carefully examining the feasibility of opening an investigation into migrant-related crimes in Libya should the court’s jurisdictional requirements be met,” Bensouda said.

The United Nations Security Council asked the court in 2011 to investigate crimes committed since the start of an uprising the same year that led to the fall of leader Muammar Gaddafi. The oil-producing North African state slipped into turmoil and been riven by factional strife since then.

The International Criminal Court, which opened in 2002, has international jurisdiction to prosecute genocide, crimes against humanity and war crimes in member states or if a situation is referred by the U.N. Security Council.