The logs seen by the paper reveal that most CIA planes landed in Germany, which saw 96 visits, and Britain, which had 80 planes stopping over.

The report suggests that European airports have been frequently facilitating the transport of suspected terrorists by the CIA to the Guantanamo Bay camp, or possibly to alleged secret prisons somewhere in eastern Europe.

The Washington Post reported in November on the existence of such secret prisons, with leading NGO Human Rights Watch subsequently identifying EU member state Poland and candidate state Romania as likely locations for the camps.

But the flight records reportedly show only one CIA visit to the Polish Szymany airbase, which had been earmarked as one such location.

CIA planes, some of them known to be implicated in the practice of "rendition" (the extra-judicial seizure of terror suspects), have recently been reported to have landed at airports across Europe.

Meanwhile, Washington has come under increasing pressure to provide clarification over the matter, shortly before a visit by Ms Rice to Europe next week.

The US foreign secretary is also due to visit NATO in Brussels on Thursday (8 December) and will stop over in Germany, Ukraine and Romania, one of the countries identified as a possible location of CIA jails.

State Department spokesman Sean McCormack said the administration would respond "to the best of our ability" to a letter sent to Washington by UK foreign minister Jack Straw on behalf of the EU, expressing concern about possible "violations of international law".

The Washington Post highlights that the affair could have a far-reaching negative impact for US diplomatic relations with even its staunchest European allies, such as the Netherlands.

Dutch foreign minister Bernard Bot said before the Dutch parliament last week that if the reports on the alleged existence of CIA prisons in Europe were found to be true, this would have "consequences" for Dutch participation in military operations in Afghanistan.