London ? Human rights workers and 20 former inmates at Guantanamo Bay and other U.S. terror-suspect prisons abroad convened a conference here Friday to bring new pressure on Washington to end what they called systematic torture and unjustified detention.

“Torture should have been kept where it belonged, in the 16th century, instead of being imported into the 21st,” said Irene Khan, secretary general of Amnesty International, which is co-hosting the meeting. Ten other foreign prisoners will testify by videotape, in what organizers call the largest gathering ever of former Guantanamo prisoners and prisoners’ families.

The conference opens as the Bush administration is facing increasing criticism abroad over its open-ended detention of terror suspects. U.S. officials contend that the unique threat that international terror groups pose to the U.S. justifies continued operation of the prisons. Inmates are treated humanely, officials have said, and when reports of mistreatment surface, prompt legal action is taken against the perpetrators.

The White House is also taking criticism because of a report in The Washington Post that the CIA has been interrogating top al-Qaida captives in secret prisons in countries that at various times have included Thailand, Afghanistan and several in Eastern Europe.

At a news conference, Khan called for the European Union and the United Nations to launch an investigation into which countries are hosting the secret CIA prisons. “It’s about time that this veil of secrecy is broken,” she said.