European Union Justice Commissioner Franco Frattini threatened sanctions for any EU nation found to have allowed secret CIA prison camps to operate on their soil.
"Should the accusations be accurate, I would be forced to draw serious consequences," Frattini said at a security conference in Berlin.
He said that any EU country found to have harbored one of the reported prison camps could have their voting rights in the Council of Ministers, the body which groups the 25 EU heads of government, suspended.
Frattini said the operation of such camps on EU soil would violate the bloc's rules governing freedom and human rights.
The EU had made contact several days ago with the White House about possible secret CIA activities in Europe, but Washington had "unfortunately not yet given any formal assurance" that the reports were untrue, he said.
The US State Department said Monday it was ready to answer queries "in as complete and forthright a manner as we possibly can" as Secretary of State Condoleezza Rice announced a trip to Europe next week.
"We have received inquiries from Europe concerning these press reports," State Department spokesman Sean McCormack said.
"We're going to do our best to answer these questions in as complete and forthright a manner as we possibly can."
McCormack said that Rice, due to visit Germany, Romania and Ukraine before heading to Belgium for a NATO meeting, was prepared to discuss the reported secret prisons if asked by her country's allies.
But he gave no indication whether she would go beyond the US administration's line, neither confirming nor denying the existence of the interrogation centers.
The Council of Europe's parliamentary assembly had already announced a probe into reports of the CIA operating clandestine prisons in some European countries.
Germany and other EU countries are demanding the US government provide "clarifications" after reports that the CIA flew suspected Islamist extremists to secret prisons in Europe.
Germany has already opened an investigation into a case in which an Egyptian suspect was transported via Ramstein in western Germany, the largest US airbase in Europe, to Egypt where his supporters say he was tortured.
A number of other European countries have opened inquiries into alleged CIA plane landings, including Finland, Hungary, Iceland, Italy, Norway, Poland, Portugal, Romania, Spain and Sweden.
New German Foreign Minister Frank-Walter Steinmeier was expected to raise the issue of the flights when he meets Rice in Washington on Tuesday.
His deputy minister, Guenter Gloser, said he believed Steinmeier would push Washington for an explanation.
"Against the backdrop of this debate, we will be looking for ways to clear up this issue," Gloser told Bayerischer Rundfunk radio.
Steinmeier said in an interview published Sunday that he was concerned by the CIA plane accounts but would reserve judgment until Washington addressed the subject.
German Defence Minister Franz Josef Jung, on a visit to Paris on Monday, said his country wanted to know if "acts of torture" had taken place.
"That's the point that worries us, legitimately I think. I hope that all this can be explained away," Jung said.
Meanwhile the German government's coordinator for transatlantic relations, Karsten Voigt, said US lawmakers could put more pressure on President George W. Bush than European politicians.
"We can count on the fact that this will be probed by the American public, particularly by the US Congress," Voigt told Deutschland Radio Kultur.
(Chinadaily.com via agencies November 29, 2005)