BAGHDAD — An al-Qaida front group in Iraq claimed responsibility for a bloody attack on a government compound in the Islamist militants’ former stronghold west of Baghdad last month and vowed more attacks on the Shiite-led government as it tries to make up with its Sunni-backed members.

Seven policemen were killed in a three-hour battle between Shiite-dominated security forces and Sunni militants Jan. 15 in the Anbar provincial capital of Ramadi, 70 miles west of Baghdad. It was the first serious gunbattle for Iraqi forces against insurgents without American backup.

Violence has surged since the U.S. completed its military withdrawal from Iraq in December. The country has also been plunged into a political crisis after the Shiite-led government issued an arrest warrant for the Sunni Vice President Tariq al-Hashemi on terrorism charges. Security forces have detained hundreds of Sunnis suspected of ties to the deposed Baath Party of Saddam Hussein.

A statement by al-Qaida’s Islamic State of Iraq late Tuesday praised the attackers in Ramadi as a “group of the heroes” for targeting Iraqi troops, who it said were agents of Iran. The group vowed more attacks, saying the recent blasts were “very small” compared to those coming.

Al-Qaida was one of the main U.S. enemies in Iraq. It was behind some of the deadliest attacks on U.S. soldiers, Iraqi security forces and American-backed government institutions.

Since the U.S. pullout, al-Qaida and other Sunni militants have stepped up attacks on Shiites raising concern that the surge in violence — combined with a sectarian crisis in the government — might deteriorate into a civil war.