Switzerland has demanded answers from the United States following claims that suspected terrorists have been flown through Swiss airspace to secret prisons.
It comes as US Secretary of State Condoleezza Rice visited Germany on Tuesday for talks dominated by the row over CIA-organised prisoner flights.
The Swiss branch of Amnesty International is also applying pressure after Foreign Minister Micheline Calmy-Rey confirmed in parliament on Monday that questions have been raised with the US.
The foreign ministry has twice sought clarification about four alleged CIA flights touching down at Geneva airport and some 30 other flights passing through Swiss airspace. But Washington has yet to respond to the questions.
Foreign ministry spokeswoman Carine Carey told swissinfo that the Swiss embassy in Washington raised concerns with the US State Department in mid-November.
"These over-flights and landings in Switzerland are alleged to have transported prisoners, and this is one of the points [for which] we have asked for clarification," she said.
"The flights concerned have been declared as private flights and we have no knowledge about their aims or the identity of the passengers on board. Switzerland does not know if the CIA organised these flights – this is another question that has been addressed to the US.
"If these allegations were to be confirmed then Switzerland would condemn these practices, but there has been no concrete evidence so far."
Veil of secrecy
The Swiss branch of Amnesty International is concerned about the shroud of secrecy surrounding the flights.
"We are asking questions and we are putting pressure on the Swiss government to get information," spokesman Jürg Keller told swissinfo.
"If these flights do contain prisoners then we have no way of knowing if they are being tortured or if they have access to legal advice."
Rice's visit to Europe has been dogged by controversy after the Washington Post newspaper printed allegations of secret prisoner camps in eastern Europe.
Swiss parliamentarian Dick Marty is currently leading a Council of Europe investigation into the allegations.
Rice has repeatedly denied that prisoners are tortured but drew criticism when she referred to the movement of suspected terrorists as "renditions".
The US embassy in Bern told swissinfo that they had forwarded concerns about flights from the Swiss authorities to Washington in the summer. But a spokesman declined to comment further.
Carey said Switzerland is opposed in principle to the secret detention of prisoners.
"The detention of prisoners in secret places represents, for Switzerland, a violation of human rights and fundamental freedoms, when prisoners are deprived in this way of a due protection as guaranteed by the law.
"In the fight against terrorism, human rights and international humanitarian law must be respected," she said.
swissinfo, Matthew Allen
Switzerland has asked for details from the US authorities over four recorded landings at Geneva airport and 30 flights in Swiss airspace.
The Washington Post reported on November 2 that the US is using "Soviet-style" prison camps to interrogate suspected terrorists in eastern Europe.
US Secretary of State Condoleezza Rice labelled the movement of suspected terrorists as "renditions" in a speech made on Monday.