The United Nations says it has found a bugging device in a room at its European offices in Geneva.
The room was used by ministers and heads of delegations
The revelation, first made on Swiss television, was confirmed in a statement by a UN spokeswoman.
She said the device was found recently during repairs to the French Hall, often used for video conferences with the UN headquarters in New York.
The room is reported to have been used by ministers from major powers last year during private talks on Iraq.
The UN spokeswoman, Marie Heuze, said an inquiry had failed to determine who planted the device.
A Geneva-based security expert who saw photos of the device told Television Suisse Romande that the system appeared to be of Russian or Eastern European origin.
"It's a very sophisticated piece of listening equipment
where the sound is picked up and immediately
retransmitted," Surveillance Consulting Group head Patrick Daniel Eugster said, according to the Associated Press news agency.
Its size indicated it was three or four years old, he added.
There have been allegations in the past that senior UN officials were bugged during the run-up to the Iraq war by countries such as Britain and the United States.