Baghdad ? An al-Qaida-linked suicide bomber struck a safehouse occupied by an insurgent group that has turned against the terror network. Friday’s attack northeast of Baghdad killed two other militants, police said, the latest sign that an internal Sunni power struggle is spreading.

The U.S. military also announced the deaths of five more servicemen. At least 126 American troops were killed in Iraq in May, the third-deadliest month for U.S. forces since the war began more than four years ago.

The explosion in Baqouba came as Iraqi and U.S. troops fanned out in the Sunni stronghold of Amariyah in the capital, enforcing an indefinite curfew after heavily armed residents clashed with al-Qaida in Iraq fighters, apparently fed up with the group’s brutal tactics.

With the insurgency appearing increasingly fragmented, Iraqi officials congratulated Amariyah residents for confronting al-Qaida.

“Government security forces are now in control of the Amariyah district,” Iraqi military spokesman Qassim al-Moussawi was quoted as saying by Iraqi state TV. He also lauded “the cooperation of local residents with the government.”

U.S. and Iraqi officials have claimed recent success in the effort to isolate al-Qaida, particularly in the western Anbar province, where many Sunni tribes have banded together to fight the terror network.