NAJAF, Iraq, Jan 28 (Reuters) - Iraqi security forces were fighting a group of Sunni insurgents holed up in orchards in the Shi'ite holy city of Najaf on Sunday, the provincial governor said, and a witness reported seeing a helicopter come down. A Reuters reporter at an army checkpoint about 1.5 km (one mile) from the fighting said he heard a burst of machinegun fire and saw smoke coming from a U.S. attack helicopter circling above the battle. He said the helicopter, which had been rocketing the militants, came down and smoke was rising from the site. It was not immediately clear whether it had crashed, he said. Police in Najaf, seat of Iraq's most powerful Shi'ite clerics, refused comment on the fighting and the U.S. military said they did not issue statements on ongoing operations. An officer in the Iraqi Army's 8th Division in Najaf, who declined to be named, said he had also heard a report of a downed helicopter. He said the gunmen were dressed in camouflage uniforms and appeared to be well organised and fighting in small formations. Governor Asaad Abu Gilel told Reuters the authorities had uncovered a plot by the fighters to kill some of the clerics on Monday, the climax of the Shi'ite mourning ritual of Ashura, a high point of the Shi'ite religious calendar. The Reuters reporter said he could hear intense gunfire. He said he had earlier seen two wounded soldiers with a dead comrade in the back of a truck outside an Iraqi military base. He said troop reinforcements from the nearby city of Hilla were on their way and he had heard radio communications in which soldiers in the midst of the fighting were asking for fresh ammunition supplies. Abu Gilel said the militants, who included foreign fighters, had arrived in the city disguised as pilgrims in recent days and based themselves in the orchards, which he said had been bought three or four months ago by supporters of Saddam Hussein. Iraqi forces had now surrounded the orchards and were battling the militants. No U.S. troops were involved in the operation, but U.S. helicopters were providing air support, he said. U.S. forces largely withdrew from Najaf province last month. "There is a conspiracy to kill the clergy on the 10th day of Muharram," he said, referring to the day of the Muslim calendar on Monday. The climax of Ashura, it is the anniversary of the 7th century Battle of Kerbala which helped consolidate the schism between Shi'ite and Sunni Islam. Abu Gilel said there were casualties in the clashes, but he could not say how many. A spokesman for the Najaf governorate, Ahmed Diabil, said five people had been detained. An Iraqi army officer, who declined to be named, said 25 people had been detained.
