Turkish authorities discovered a vehicle full of explosives at Istanbul's international airport Friday, television station CNN Turk said, but an airport official told Reuters that investigators had so far found no evidence of a bomb. "Security received a warning and closed the car park for 1-1/2 hours. At this time, they have been unable to find any explosive device," the official said. CNN Turk said the suspect vehicle had been parked in the airport's public garage. The bomb squad had also destroyed a remote-controlled explosive device found in the garage, it said. It was not clear if it was in the same vehicle. Turkey's largest city is on edge before a NATO summit next week to be attended by President Bush and more than 40 other world leaders. 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 Thursday in Istanbul. Authorities have blamed left-wing extremists for the attack. **PHOTO CAPTION*** The bomber behind a blast in Istanbul that killed four people just four days before the city hosts a NATO summit was a woman in her twenties from the mainly Kurdish southeast, Turkish authorities said June 25, 2004. (Reuters)