US and Iraqi forces met armed resistance on the first day of a major offensive near the Syrian border aimed at destroying an Al-Qaeda stronghold.

Dubbed Operation Steel Curtain, the sweep comprises about 3,500 troops and includes for the first time several battalion-sized units of Iraq"s military in joint operations in the vast Sunni dominated western Al-Anbar province.

US and Iraqi forces "have encountered sporadic resistance -- mostly small arms fire and improvised explosive devices -- from Al-Qaeda in Iraq-led insurgents throughout the city," the military said late Saturday.

There were no reports of military or civilian casualties but there was an undetermined number of insurgent casualties, the military said.

At least nine air strikes were called on positions described as "enemy strong points," and a separate strike was carried out against a suspected car bomb.

"Only buildings occupied by insurgents firing on marines and Iraqi soldiers have been targeted," the military said.

Iraqi scouts, described as "specially recruited soldiers from the Al Qaim region," are embedded with the front-line units "and are helping to identify insurgent strong points and areas known to contain these homemade bombs."

US officials have long held that the most serious insurgent acts in Iraq are carried out by foreign Al-Qaeda operatives, most of whom they say cross from Syria via the Euphrates valley.

The area along the 600-kilometer (370-mile) border with Syria is renowned for illegal trade, with cross-border smuggling a way of life for many of the local tribes.

The operation involves 1,000 Iraqi army soldiers as well as 2,500 Marines, sailors and soldiers in what the military called "the largest concentration of Iraqi army forces to take part in an operation in Al-Anbar this year."

Steel Curtain follows two earlier operations, Iron Fist and River Gate, also along the Euphrates valley in the restive Al-Anbar province.

It is also designed to "establish a joint permanent security presence along the Syrian border," something lacking in previous operations.

The border smuggling routes are also open to foreign insurgents, 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 means, the demolition experts," he said.

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

Meanwhile the US military announced four US soldiers were killed in separate incidents across Iraq on Friday and Saturday.

The deaths bring to 2,045 the number of US military personnel who have died in Iraq since the March 2003 invasion, according to an AFP tally based on the Iraq Coalition Casualty Count, an independent group that follows US casualties in Iraq.

Abu Musab al-Zarqawi"s Al-Qaeda in Iraq on Saturday claimed it executed 15 Iraqi soldiers kidnapped while on leave two days ago west of Baghdad, according to an Internet statement which could not be independently verified.

On Friday, the group warned diplomats in Baghdad to "pack their bags and leave" or face certain death, after claiming a day earlier it had decided to kill two Moroccan embassy employees held hostage for being "loyalists of the oppressors and elements of the apostate regime in Morocco."

In Rabat, the Moroccan foreign ministry scoffed at the idea of closing its Baghdad embassy.

Al-Qaeda in Iraq "has nothing to teach Morocco," and Rabat will not succumb to "blackmail," especially "coming from a terrorist group which cannot claim to represent Iraq," the ministry said.

Al-Qaeda in Iraq also claimed it shot down a US helicopter with an anti-aircraft missile in the Al-Anbar province town of Ramadi on Wednesday. Two US marines died in the attack.

US Army General Rick Lynch said the AH-1 Super Cobra, which had been flying low supporting ground troops, indeed may have been shot down.

In other violence, 11 members of the same family were killed and three wounded when armed men ambushed their minibus northeast of Baghdad, officials said.

Meanwhile, the White House said that Iraqi Deputy Prime Minister Ahmed Chalabi will meet US Treasury Secretary John Snow and Secretary of State Condoleezza Rice when he travels to Washington later this month -- but not with President George W. Bush.

Chalabi was once a Pentagon favorite who provided volunteers for the embryo of an Iraqi force during the 2003 US-led invasion, as well as erroneous information on Saddam"s weapons of mass destruction.

But he fell out of US favor amid charges last year that he traded US intelligence to Iran.