Greek Prime Minister Costas Karamanlis and several ministers had their mobile phones tapped for more than a year, the government has confirmed.
Costas Karamanlis and other ministers were tapped
A spokesman said an investigation had been opened, but had not yet discovered who was conducting the surveillance.
The taps are reported to have begun before the Athens Olympics in 2004 and lasted until March last year.
They were detected by a telephone company manager dealing with customers who had reported technical problems.
About 100 mobiles belonging to politicians from both parties are thought to have been monitored.
"The phones tapped included the prime minister's, those of cabinet members, one former minister, now in opposition, and others," government spokesman Theodore Roussopoulos told reporters.
"The phone tapping was carried out by unknown person or persons using high technology."