The OH-58 Kiowa chopper, attached to the 101st Airborne Division, went down at 1730 GMT northwest of the city of Kayyarah, killing the two crew on board.

The cause of the crash was not immediately known but an accompanying helicopter did not report "hostile activities", the spokesman added.

It was the fourth such crash since the beginning of January.

A US AH-64 Apache helicopter crashed on 13 January, after a suspected downing by resistance fighters in the restive western district of Fallujah.

Nine US soldiers were killed when a Black Hawk helicopter was hit by fire near Fallujah on 8 January.

And one soldier died and another was wounded when ground fire struck a Kiowa on 2 January.

Ansar al-Islam

Ansar al-Islam are accused of
having ties to al-Qaida

Meanwile, US Special Forces troops have captured a leading figure in Ansar al-Islam, an anti-American guerrilla group operating in Iraq, a US official said on Friday.

The US government says Ansar has ties to the al-Qaida network, although this remains unproven. 

Husam al-Yameni was taken into custody during an operation last week near the town of Fallujah, 50km west of Baghdad, said the official.

"There's a strong possibility that this guy was involved in some of the major attacks in Iraq," he said.

The official described al-Yemeni as a top associate of Abu Musab Zarqawi - who is suspected of plotting the murder of a US diplomat in Jordan, overseeing a training camp in Afghanistan, and having links to al-Qaida.

The United States last year offered a reward of up to $5 million for information leading to the arrest or conviction of Zarqawi.

The US official said al-Yemeni was the highest ranking member of Ansar al-Islam captured to date.