(Updates with casualty toll) BAGHDAD, March 25 (Reuters) - U.S. and Iraqi troops clashed with gunmen in a town south of Baghdad on Sunday shortly after a Sunni mosque was set ablaze in an apparent revenge attack for the destruction of a Shi'ite mosque in the town a day earlier. Gunmen stormed the Sunni mosque in Haswa, a religiously mixed town about 50 km (35 miles) south of the Iraqi capital, on Sunday morning and destroyed its minaret in a blast. The building was set on fire, a police official said. They said at least four people were wounded. A second Sunni mosque was attacked but damage was reported to be minor. A suicide truck bomber exploded outside a Shi'ite mosque in Haswa on Saturday, killing 14 and wounding 21, Hilla police said. The provincial health directorate and Baghdad police put the toll at 16. Only the mosque's minaret was left standing. As Shi'te residents combed through the rubble of the building on Sunday, a column of armoured U.S. and Iraqi Humvee vehicles nearby came under machinegun fire. U.S. troops could be seen running into buildings nearby. The area was rocked by an explosion that sent a large cloud of dust into the air. The cause of the blast was not immediately clear. There were no immediate reports of any casualties. Police in Hilla, close to the town of Haswa, said a curfew had been imposed. Mosques and other religious buildings have been frequent targets of attack. The bombing of a revered Shi'ite shrine, the al-Askariya mosque, in the town of Samarra in February 2006 sparked a wave of sectarian fighting between Iraq's majority Shi'ites and minority Sunnis that has killed tens of thousands.
