A force of 1,000 US soldiers launched Operation 'Iron Fist' in and around the village of Sadah in the restive Euphrates Valley on Saturday, the latest offensive aimed at rooting out Al-Qaeda-linked insurgents in the border region.

On Sunday morning, "seven terrorists were engaged by Marine aircraft west of Sadah," the US military said in a statement.

"Four were killed and three fled into a nearby building with an estimated nine additional fighters. When the terrorists began firing, aviation assets were again called in and the number of casualties are unknown at this time," it added.

Later in the day, in another engagement near Karabilah, marines were engaged by rocket propelled grenades and gunfire from a building and returned fire killing eight, the military said.

US forces also wounded five civilians, one of them seriously, when a tank, responding to gunfire, fired a shell into a building in the Sadah area, the military said.

Four insurgents were detained on Sunday, the military said.

On Saturday, the first day of operations, the US military said it had killed eight rebels.

A marines' statement said there were no casualties among the US force.

Responding to an internet-made claim, the marines also said "there are no indications that Al Qaeda claims of having kidnapped two Marines in western Iraq are true."

"Multi-National Force West is conducting checks to verify all Marines are accounted for," a statement added.

Al-Qaeda's branch in Iraq said in an Internet statement Sunday that it had abducted two US marines involved in the offensive and threatened to kill them unless US forces release female Sunni Muslim prisoners within 24 hours.

"The Al-Qaeda soldiers were able to take two so-called 'marines' captive after they encircled a foot patrol of the crusaders in the western region," said Abu Musab al-Zarqawi's Al-Qaeda Organisation in the Land of Two Rivers.

The statement, whose authenticity could not be confirmed, said the patrol was taking part in "the so-called 'Iron Fist'" offensive along the Syrian border.

"Al-Qaeda Organisation in the Land of Two Rivers gives the crusaders 24 hours to release Sunni Muslim women from their and their (Shiite) lackeys' prisons," in Iraq, said the statement on an Islamist website.

The statement warned that unless the women prisoners were freed, the US army should "not bother to look for their sons."

"Let it be known to them that the mujahedeen (holy warriors) are itching to slaughter those (alleged hostages)... to avenge the blood of the Sunni people being shed at their (Americans') hands and the hands of their stooges in the apostate (Iraqi) government," the statement said.