The goal of Operation Steel Curtain is "to restore security along the Iraqi-Syrian border and destroy the al-Qaida in Iraq terrorist network operating throughout Husaybah, located on the Iraqi-Syrian border", the military said on Saturday.

The offensive, near the border town of al-Qaim and about 320km west of Baghdad, involves about 1000 Iraqi army soldiers as well as 2500 US marines, sailors and soldiers.

"Operation Steel Curtain marks the first large-scale employment of multiple battalion-sized units of Iraqi army forces in combined operations" with US-led forces, the military said.

The US military has long held that the most serious attacks in Iraq are being carried out by foreign al-Qaida operatives, most of whom cross from Syria via the Euphrates valley.

Poor town

In al-Qaim, a witness said the offensive in Husaybah began by about dawn with four loud explosions, apparently caused by US warplanes or helicopters.

The witness said the telephone service to the town was cut. He spoke on condition of anonymity out of concern for his safety. Husaybah is a poor Sunni Arab town of about 30,000 people.

It is located near the Euphrates river and surrounded by bleak hills and desert terrain.

Most residents live in small brick and concrete homes, and many may have fled during another US offensive in the area last month.

US soldier killed

Elsewhere, a US army soldier working with Task Force Baghdad was killed by small-arms fire south of the capital on Friday, the military said.

The death raised to 2043 the number of members of the US military who have died since the beginning of the Iraq war in March 2003, according to an Associated Press count.

Combat operations by Task Force Baghdad soldiers also found and destroyed stockpiles of weapons and munitions from fighters in and around the capital on Thursday and Friday, including rockets, homemade bombs, mortars, rocket-propelled grenade launchers, grenades and ammunition, the US command said.

Threat to diplomats

Al-Qaida in Iraq, which is led by the Jordanian Abu Musab al-Zarqawi, warned this past week that foreign diplomats should leave Iraq or face attacks.

The group also said it would kill two kidnapped Moroccan Embassy employees.

The Moroccans, driver Abderrahim Boualam and embassy staff member Abdelkrim el-Mouhafidi, disappeared on 20 October while driving to Baghdad from Jordan.

The authenticity of the two al-Qaida in Iraq statements could not be independently confirmed.

Cross-border smuggling

Steel Curtain follows two earlier operations, Iron Fist and River Gate, also in the western Sunni Arab province of al-Anbar.

The area along the 600km border with Syria is renowned for illegal trade, with cross-border smuggling a way of life for many of the local tribes.

The smuggling routes are also open to foreign fighters, mainly from other Arab countries, albeit crossing in small numbers, Marine Colonel Stephen Davis told AFP earlier.

"They do not bring battalions, they bring the leadership, the financial man, the demolition expert," he said.

Davis said the marines patrolling the border "have intercepted mass ammunition supplies" and even anti-aircraft weapons.