Iraqi officials claimed Monday that 300 militants were killed in a fierce battle between US-backed Iraqi troops and insurgents allegedly plotting to kill pilgrims at a major Shi'ite Muslim religious festival, while bombings and mortar attacks targeting Shi'ites elsewhere killed at least 15 people. The fighting that began Sunday near the Shi'ite holy city of Najaf had largely subsided by Monday as Iraqi security forces frisked suspects, including several men forced to lie down on a road between a bus and a motorcycle, while others patrolled elsewhere on the battlefield. A US helicopter crashed during the fight, killing two American soldiers whose bodies were recovered, the military said. The statement did not give any information on why the aircraft crashed - the second US military helicopter to go down in eight days. Ahmed Deaibil, a spokesman for Najaf province, said the fighting had continued until 4 a.m. Monday, but US and Iraqi forces still had the area surrounded and had seized heavy machine guns, ammunition and other weapons. Citing reports from commanders on the ground, he said 300 militants had been killed and 13 arrested, while the casualty toll for Iraqi forces was three soldiers and two policemen killed and 30 wounded. Brig. Gen. Fadhil Barwari also said 300 militants had been killed, including 30 Afghans and Saudis, and 20 were captured. Iraqi security officials said earlier that one Sudanese was among the fighters detained. The figures could not be independently confirmed. The Iraqi Defense Ministry, which oversees the army, said it could not yet give a casualty toll because sporadic fighting was ongoing. Attacks, meanwhile, struck Shi'ite targets in the Baghdad area as the Islamic sect marks Ashoura, the holiest day in the Shi'ite calendar commemorating the 7th century death of Imam Hussein. The celebration culminates Tuesday in huge public processions in Najaf, Karbala and other Shi'ite cities. The mortar rounds rained down on a Shi'ite neighborhood in the Sunni-dominated town of Jurf al-Sakhar, 70 kilometers south of Baghdad, Monday morning, police spokesman Capt. Muthanna Khalid said. He said 10 were killed, including three children and four women, and five other people were wounded. A wounded boy lay next to his blood-stained father at a hospital in the nearby town of Musayyib, while six bodies were covered with blankets in the morgue. The strike came a day after mortar shells hit the courtyard of a girls' school in a mostly Sunni Arab neighborhood of Baghdad, killing five pupils and wounding 20. UN officials deplored Sunday's attack, calling the apparent targeting of children "an unforgivable crime." A parked car bomb also struck a bus carrying Shiites to a holy shrine in northern Baghdad on Monday, killing at least four people and wounding six, police said. The blast occurred when a small car parked nearby exploded about 9:30 a.m. as the pilgrims were boarding the bus on Palestine Street. The bus, which was completely burned out, had been heading to Kazimiyah, which is home to the most important Shi'ite mosque in the capital. Elsewhere, a bomb hidden under a concrete barrier exploded as workers were paving a street in an intersection in a predominantly Shi'ite area in eastern Baghdad, killing one worker and wounding two others, police said. Authorities said Iraqi soldiers supported by US aircraft fought all day Sunday with a large group of insurgents in the Zaraq area, about 12 miles northeast of the Shi'ite holy city of Najaf. Provincial Gov. Assad Sultan Abu Kilel said the assault was launched because the insurgents planned to attack Shi'ite pilgrims and clerics during ceremonies marking Ashoura. Officials were unclear about the religious affiliation of the militants. Although Sunni Arabs have been the main force behind insurgent groups, there are a number of Shi'ite militant and splinter groups that have clashed from time to time with the government. Iraqi soldiers attacked at dawn and militants hiding in orchards fought back with automatic weapons, sniper rifles and rockets, the governor said. He said the insurgents were members of a previously unknown group called the Army of Heaven. "They are well-equipped and they even have anti-aircraft missiles," the governor said. "They are backed by some locals" loyal to ousted dictator Saddam Hussein. The mortar attack in Baghdad occurred about 11 a.m. Sunday at the Kholoud Secondary School in the Adil neighborhood, police and school officials said. The principal, Fawzyaa Hatrosh Sawadi, said students were mingling in the courtyard during a break in exams when at least two shells exploded. No group claimed responsibility for the attack, but a Sunni organization, the General Conference of the People of Iraq, blamed Shi'ite Muslim militias with ties to government security forces. The group said the mortar shells bore markings indicating they were manufactured in Iran, which US officials accuse of supporting Shi'ite militias. The mortar attacks and bombings appeared to be part of the sectarian reprisal killings that have pushed Iraq into civil warfare over the past year, violence that US President George W. Bush hopes to quell by sending up to 21,500 more American soldiers to Baghdad and surrounding areas. US officials have long accused al-Qaida in Iraq, a Sunni Muslim group, of fanning sectarian hatreds by staging vicious attacks on Shi'ite civilians. Revenge killings have surged since the bombing of a Shi'ite shrine in the largely Sunni city of Samarra last February 22.