ISLAMABAD, Pakistan —  An attempt to bomb Islamabad International Airport was thwarted Saturday when a security guard found an abandoned briefcase and threw it into an outside garbage can, where it exploded.

Police said the briefcase was discovered in the airport's VIP lounge. The blast damaged some nearby vehicles but caused no injuries, police said. It was unclear what kind of explosives were inside the briefcase.

The briefcase was found about 1 p.m. in the departure area by a security guard, who removed it within moments of the blast, police said.

It was unclear who left the briefcase or how long it was there before it was detected.

Pakistani security has been stepped up since the beginning of U.S.-led airstrikes in neighboring Afghanistan. Militant Muslims oppose the government's backing for the U.S. campaign.

The Associated Press contributed to this report.