Iraq ? A bomb-rigged truck exploded at a checkpoint Tuesday near the western city of Ramadi, killing two U.S. Marines and wounding three others in an apparent strike by al-Qaida in Iraq in one of its former strongholds. The U.S. toll in the war rose to 4,044.

At least one civilian also died and two dozen were injured in the blast, the latest in a string of recent strikes in areas where local Sunnis have joined U.S. forces to battle al-Qaida.

Al-Qaida has been regrouping after suffering a devastating blow last year when thousands of Sunni tribesmen turned against them. Last weekend, al-Qaida announced a one-month offensive against U.S. troops and Sunnis who have joined forces with Americans.

Osama bin Laden’s deputy, Ayman al-Zawahri, said in an audiotape posted Tuesday on the Internet that al-Qaida-led insurgents in Iraq were the “primary force” in battling the Americans and “challenging Iranian ambitions” in Iraq.