Aid groups are suing the French government to stop the donation of six boats to Libya's navy, saying the watercraft will be used to take migrants to detention centers notorious for horrific conditions.

Europe has relied heavily on the Libyan coast guard, which is part of the navy, to intercept migrants bound for Europe and return them to the detention centers, where disease is widespread and migrants say they face routine abuse. Conditions have deteriorated further in recent weeks as fighting has erupted between rival militias.

The U.N. says some 3,600 refugees and migrants are detained near the front lines. The lawsuit filed Thursday by eight aid groups seeks a stay on the boat donation, saying it violates the European embargo on Libya and makes France complicit in the abuse.