BAGHDAD, Iraq — Iraqi officials said today that 300 militants were killed in a fierce battle between U.S.-backed Iraqi troops and insurgents allegedly plotting to kill pilgrims at a major Shiite Muslim religious festival. Elsewhere, bombings and mortar attacks targeting Shiites killed at least 15 people.

The fighting that began Sunday near the Shiite holy city of Najaf had largely subsided by today as Iraqi security forces frisked suspects while others patrolled elsewhere on the battlefield.

A U.S. 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 U.S. military helicopter to go down in eight days.

Ahmed Deaibil, a spokesman for Najaf province, said the fighting had continued until 4 a.m. today, but U.S. 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 Shiite targets in the Baghdad area as the Islamic sect marks Ashoura, the holiest day in the Shiite calendar commemorating the 7th century death of Imam Hussein. The celebration culminates Tuesday in huge public processions in Najaf, Karbala and other Shiite cities.

Mortar rounds rained down on a Shiite neighborhood in the Sunni-dominated town of Jurf al-Sakhar, 40 miles south of Baghdad, this 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. U.N. officials deplored Sunday's attack, calling the apparent targeting of children "an unforgivable crime."