Fourteen pounds of powerful explosives were found at Istanbul's airport on June 25, two days before President Bush arrived for a NATO summit and two hours before Turkey's prime minister landed at the heavily guarded facility, police confirmed on Friday.

The bomb was defused after being discovered in a parking garage, packed in a spare tire beside a parked car and linked to a cell phone for detonation by remote control, according to security officers and media reports. A U.S. law enforcement official said such a bomb "would have had a devastating effect."

Turkish and U.S. officials had repeatedly denied reports of the discovery, apparently in an effort to contain embarrassment at the security breach on the eve of a summit attended by more than 40 prime ministers and presidents.

The discovery was confirmed by a police spokesman on the day a car bomb killed at least six people in the eastern city of Van. That attack targeted the motorcade of the provincial governor, who escaped unharmed.

Police initially blamed Kurdish separatists, but the Kurdistan Workers' Party -- the guerrilla group that, using the new name Kurdistan Freedom and Democracy Congress, recently resumed attacks on government forces in southeastern Turkey -- denied blame.

The flurry of bombings has revived security concerns across Turkey, whose vital tourist industry was hurt when four massive car bombs killed more than 60 people in Istanbul last November. Those blasts, which were attributed to Turkish militants funded by al Qaeda, raised concerns that Islamic radicals might target the NATO summit last Monday and Tuesday.

But leftist groups asserted responsibility for three small blasts that marred the gathering, including an explosion aboard a Turkish Airlines jet about three hours before Bush left from the same airport.

Explosives hidden in a woman's wallet blew off the fingers of the cabin cleaner who found it after passengers left the plane. The device was apparently the first bomb smuggled aboard a commercial airliner since Richard Reid tried to ignite a bomb hidden in his shoe on a Miami-bound American Airlines flight in December 2001.

A Marxist group said it was responsible for the Turkish Airlines bomb and for the device found in the parking garage, boasting of its ability to best Turkish security efforts. The bombs reportedly were fashioned from the same unstable explosive amalgam used by Reid.

"We went in there despite the intensive security measures called 'zero risk,' " said a statement issued by the Armed Forces of the Poor and the Oppressed.