BRUSSELS (Reuters) - European governments are complicit in grave human rights violations in Libya through their support for authorities there who often work with people smugglers and torture refugees and migrants, Amnesty International said on Tuesday.

Amnesty said up to 20,000 people are now held in Libyan detention centers for migrants and are subject to “torture, forced labor, extortion, and unlawful killings”. Other human rights organizations have said similar things in recent months.

The European support for Libyan authorities is part of a plan to cut African immigration across the Mediterranean. It aims to lower the number of people who drown during the crossing and curb the scale of a political problem high arrivals cause to EU governments.

Italy has spearheaded the plan, in particular by training and equipping the coastguard and by spending millions to back U.N. agencies working on relief efforts in Libya.

“European governments have not just been fully aware of these abuses; by actively supporting the Libyan authorities in stopping sea crossings and containing people in Libya, they are complicit in these crimes,” said John Dalhuisen, Amnesty International’s head for Europe.

On Tuesday, Italian Prime Minister Paolo Gentiloni defended the EU’s policy in a speech to parliament ahead of this week’s meeting of the bloc’s leaders in Brussels and said sea arrivals had dropped by two-thirds since last July.

“It’s thanks to us that a light is being shone on human rights in Libya,” he said, referring to million of euros Italy and the EU spent on improving conditions for people stuck there.

A spokesperson for the bloc’s executive European Commission said: “We are aware of the inhumane and terrible conditions some face. We share the same objective as Amnesty: saving lives.”

It said the bloc’s funding helped the U.N. agency for migration, the IOM, send more than 15,000 people in Libya to their home countries in Africa. At the same time, it said the bloc has also been slowly taking in “genuine refugees”.

Libya is the main gateway for migrants trying to cross to Europe by sea, though numbers have dropped sharply since July as Libyan factions and authorities have begun to block departures under pressure from Italy, the main landing point. More than 600,000 have made the journey over the past four years.

The EU backs Libya’s coastguards in its efforts to intercept people heading to Europe but they work closely with people smugglers who torture people for money, Amnesty said.

“By supporting Libyan authorities in trapping people in Libya ... European governments have shown where their true priorities lie: namely the closure of the central Mediterranean route, with scant regard to the suffering caused,” said Dalhuisen.

Some EU officials and diplomats chafe at the bloc’s reliance on militias that have emerged since the fall of Libya’s leader Muammar Gaddafi in 2011.

But EU leaders will recommit at their meeting in Brussels on Dec. 14-15 to a strategy they say is bearing fruit in the form of fewer sea crossings.

The presidency of Libya’s U.N.-backed government said last month it was a victim of illegal migration, not a source of it, and appealed to foreign powers to help stop flows from migrants’ countries of origin.