"It is completely untrue. There is absolutely no such incident
and we are wondering where those stories are coming from," a police official from the airport told reporters on Friday. 

Istanbul Governor Muammer Guler also denied the incident, adding that authorities were investigating the source of the reports, carried earlier by the country's two main news channels, CNN-Turk and NTV. 

"There is no such thing. We expect the media not to give exaggerated reports. We are now trying to find out where this story originated from," Guler told reporters, according to the Anatolia news agency. 

CNN-Turk said security forces defused a remote-controlled bomb placed under a car in the car park of the Ataturk Airport.

The device was designed to be detonated by telephone, the channel said. NTV, meanwhile, reported the discovery of "low-impact explosives."

Even if the reports turn out to be unfounded they underscore the sensitivity of the country ahead of next week's NATO summit.

On edge

Turkey's largest city is on edge ahead of the summit to be attended by US President George Bush and more than 40 other world leaders. 

An Irish protestor gears up for
anti-Bush demonstration

Authorities have stepped up security in Istanbul, a city of more than 10 million people, conducting searches of pedestrians in public areas and searching people on the road to the airport. 

A bomb explosion killed four people, including the bomber, and wounded 21 others on Thursday in Istanbul. Authorities have blamed left-wing armed dissidents for the attack. 

Bush in Ireland

Meanwhile, Bush landed at Shannon airport in western Ireland on Friday at the start of an 18-hour visit to attend a summit between the United States and the European Union. 

His aircraft touched down just before 8:00 pm (19:00 GMT)
and he was scheduled to leave immediately for nearby Dromoland Castle, where he was due to spend the night before holding three hours of talks with EU leaders on Saturday. 

He is due to arrive in Istanbul on Sunday to attend the two-day summit starting on Monday 28 June.

Security was tight around the normally tranquil corner of
the west coast of Ireland for the Bush visit, with over 6000
police and troops deployed to keep protesters against the war in Iraq away from the president.