European lawmakers on Monday called on the European Union's executive office to conduct a formal investigation into allegations that the CIA set up secret prisons at Soviet-era compounds in Eastern Europe to interrogate Al Qaeda suspects.

Earlier this month, the European Commission promised to launch an informal probe, requesting answers from all 25 EU member states and candidate countries Romania, Bulgaria, Croatia and Turkey. But several members of the European Parliament urged the commission to open a formal investigation.

"We will only feel certain once we are sure no EU state has any link with ... detention centers where people who are detained are tortured and abused," Portuguese conservative deputy Carlos Coelho said.

Added Sarah Ludford, a British Liberal Democrat: "I am left with a sense of unease and doubt. Our mechanisms (to investigate) in the EU are inadequate. No peer review, no monitoring, no commitment."

EU Justice and Home Affairs Commissioner Franco Frattini argued it is up to individual governments to examine the allegations. He said the commission doesn't have the legal means to investigate and is only authorized by the treaties governing the EU to carry out informal, political inquiries.

"Can we seize classified filed of the CIA? No, that's not possible. We don't have the powers, we have to play it by the rules," Frattini told lawmakers.

The CIA had no comment on the decision.

A Washington Post story from Nov. 2 said the CIA has been hiding and interrogating some of its most important Al Qaeda captives in Eastern Europe, part of a covert prison system set up by the agency four years ago that at various times has included sites in eight countries. Those countries, the Post said, included several democracies.

The paper did not name the countries involved, but Human Rights Watch said it had evidence indicating the CIA transported suspected terrorists captured in Afghanistan to Poland and Romania. The conclusion was based on an analysis of flight logs of CIA aircraft from 2001 to 2004 obtained by the group.

The allegations have triggered a flurry of denials from governments in the former Soviet bloc, including Poland and Romania. Such prisons, European officials say, would violate the continent's human rights principles.

Polish independent deputy Ryszard Czarnecki noted, however, that his country's denial had referred to the present, and not to the possibility of such detention centers in the past.

Europe's leading human rights watchdog last week appointed Swiss senator Dick Marty to investigate the allegations. Marty started his work by requesting information on the issue from all 46 Council of Europe members.

The CIA has also called for a federal criminal investigation into the leak of possibly classified information on the subject to the Post.

The Bush administration has neither confirmed nor denied the Post's report.