"If Iraq is to succeed, it will need both groups to come to terms and to work together for the benefit of all Iraqis"
Iceman, Atlanta, US
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Shirwan al-Waeli, Iraq's security minister, said the group's leader "claimed to be the Mahdi".
He said the man, who is thought to have been a 40-year-old Iraqi citizen from the nearby Shia city of Diwaniya, had used the name Mahdi bin Ali bin Ali bin Abi Taleb, claiming descent from the Prophet Mohammad.
The Imam Mahdi is a ninth-century Shia spiritual leader who believers say will return at the end of time.
Al-Waeli said, "One of the signs of the coming of the Mahdi was to be the killing of the Ulema [hierarchy] in Najaf."
The group had gathered in orchards near the city and had been planning to attack the main Shia cleric leadership on Monday, an official from Najaf province said.
"Soldiers of Heaven"
The group, an obscure religious cult, included both Sunni and Shia Muslims as well as foreign nationals.
Some of the fighters wore headbands describing themselves as the Jund al-Samaa, or "Soldiers of Heaven", Iraqi officials said.
Officials said the assault was launched because the group planned to attack Shia pilgrims and senior clerics in Najaf during ceremonies marking the feast of Ashura, a Muslim holy-day.
Waeli said the death toll among Iraqi forces was around 10 soldiers and police. Najaf's police chief was also wounded, he said.
Two US soldiers were killed when their attack helicopter came down during the fighting, military sources said.
Iraqi officials and witnesses said it appeared to have been shot down.
Among previous violent instances of people claiming to be the Mahdi were an opposition movement to British imperial forces in Sudan in the 1880s and a group of several hundred, including women, that took over the Grand Mosque in Mecca in 1979.