A suicide bomber killed at least 27 Shi'ite militiamen on the outskirts of the Iraqi town of Jurf al-Sakhar on Monday after security forces pushed Islamic State militants out of the area over the weekend, army and police sources said.
The attacker, driving a Humvee vehicle packed with explosives and likely stolen from defeated government troops, also wounded 60 Shi'ite militiamen, who had helped government forces retake the town just south of the capital.
Holding Jurf al-Sakhar is critical for Iraqi security forces who finally managed to drive out the Sunni insurgents after months of fighting.
It could allow Iraqi forces to prevent the Sunni insurgents from edging closer to the capital Baghdad, sever connections to their strongholds in western Anbar province, and stop them infiltrating the mainly Shi'ite Muslim south.
The group has threatened to march on Baghdad, home to
special forces and thousands of Shi'ite militias expected to put
up fierce resistance if the capital comes under threat.
Gains against Islamic State, an al Qaeda offshoot made up of Arab and foreign fighters, are often fragile even with the support of U.S. airstrikes on militant targets in Iraq and neighbouring Syria.
As Iraqi government soldiers and militias savoured their victory and were taking photographs of Islamic State corpses on Sunday, mortar rounds fired by Islamic State fighters who had fled to orchards to the west rained down on Jurf al-Sakhar.
The blast hit the militiamen, killing dozens and scattering body parts, according to a Reuters witness.
The next significant fighting near Baghdad is expected to take place just to the west in the Sunni heartland Anbar province.
The town of Amriyat al-Falluja has been surrounded by Islamic State militants on three sides for weeks. Security officials say government forces are gearing up for an operation designed to break the siege.
Gains in the Islamic State stronghold of Anbar could raise the morale of Iraqi troops after they collapsed in the face of a lighting advance by the insurgents in the north in June.