In what the Taliban claimed was an assassination attempt, a suicide bomber attacked the largest US military base in Afghanistan during a visit by US Vice President Dick Cheney on Tuesday, killing 23 people, including a US soldier and contractor, in a large explosion at the front gate. The bomber never got close to the vice president, who heard a loud boom but said he never felt in any danger. But the attack delivered a boost to the militants' propaganda efforts and highlighted an increasingly precarious security situation posed by the resurgent Taliban. Cheney was the highest-ranking US official to stay overnight in either the Afghanistan or Iraq war zones. The vice president had slept at the sprawling Bagram Air Base and was preparing to leave for a meeting with President Hamid Karzai when the suicide bomber struck about 10 a.m. US military officials declared a "red alert" at the base, and Cheney was rushed to a bomb shelter for a short time.