U.S. Vice President Dick Cheney met with Afghan President Hamid Karzai in Kabul today and then left Afghanistan about two hours after a suicide bombing at the main U.S. military base there killed at least 23 people. Fraudoon Pooyaa • Associated Press

Cheney was unhurt in the attack, which was claimed by the Taliban and was the closest that militants have come to a top U.S. official visiting Afghanistan. At least one U.S. soldier, an American contractor and a South Korean soldier were among the dead, NATO said.

Cheney, who visited with President Hamid Karzai and then left the country two hours after the blast, said the attackers were trying "to find ways to question the authority of the central government."

The vice president had spent the night at the sprawling Bagram Air Base, and it was about 10 a.m. when the explosion sent up a plume of smoke visible by reporters accompanying. U.S. military officials declared a "red alert."

"I heard a loud boom," Cheney told reporters. "The Secret Service came in and told me there had been an attack on the main gate."

He said he was moved "for a brief period of time" to one of the base bomb shelters near his quarters. "As the situation settled down and they had a better sense of what was going on, I went back to my room," Cheney added.

Asked if the Taliban were trying to send a message with the attack, Cheney said that fighters "clearly try to find ways to question the authority of the central government."

"Striking at the Bagram (base) with a suicide bomber, I suppose, is one way to do that," he said. "It shouldn't affect our behavior."

Maj. William Mitchell said it did not appear the explosion was intended as a threat to Cheney. "He wasn't near the site of the explosion," Mitchell said. "He was safely within the base at the time of the explosion."