Afghanistan ? Shortly before he rammed his vehicle into an American military convoy, the young bearded suicide bomber waved at Sayed Najibullah to move away. As Najibullah sped off a huge explosion ripped through a U.S. armored vehicle, killing three American troops and three Afghan civilians.

But Najibullah lived to tell the story.

Tuesday’s attack in the northern Kapisa province, which is a stronghold of insurgents loyal to the Afghan warlord Gulbuddin Hekmatyar north of Kabul, follows warnings from American military officials that more suicide attacks and roadside bombings can be expected as thousands of new U.S. troops join the fight this year.

Such attacks were up 25 percent in the first four months of 2009 compared with the same period last year.