US forces have launched a major offensive against insurgents in western Iraq near the Syrian border, with about 75 militants said to have been killed in the first 24 hours.

Military commanders said the operation, in a desert area of Anbar province north of the Euphrates River, was targeting a sanctuary for foreign insurgents and a smuggling route.

A Chicago Tribune reporter embedded with US forces said more than 1,000 American troops supported by fighter aircraft and helicopter gunships attacked villages in and around Obeidi, a city near the Euphrates River in western Iraq, not far from the Syrian border.

The offensive ``was seeking to uproot a persistent insurgency in an area that American intelligence indicated has become a haven for foreign fighters flowing in from Syria.''

The assault on the border came as US commanders said their view of the insurgency has begun to shift, with higher priority given to combating foreign fighters.

This shift comes in response to the recent upsurge in suicide attacks and other developments.

Previously, US authorities depicted the insurgency as dominated by what the Pentagon dubs ``former regime elements'' - a combination of one-time Baath Party loyalists and Iraqi military and security service officers intent on restoring Sunni rule. But since the January 30 elections, this segment of the insurgency has appeared to pull back from the fight.

Acting on the assumption that foreign fighters and Iraqi extremists might now pose the greater and more immediate threat to security in Iraq, US commanders have given orders in recent days to reposition ground forces and intelligence assets to fortify Iraq's border with Syria and block suspected infiltration routes.

They are also stepping up efforts to go after bomb-makers and organizers of suicide attacks.

In the Anbar action, US troops were north of the Euphrates, but most were stuck south of the river as engineers tried to build a pontoon bridge.

US Marines said residents of one riverside town turned off all their lights at night, apparently to warn of the approach of American forces.

Recently, US troops appear to have stepped up their attacks on suspected insurgent strongholds, including some near the Syrian border, where foreign militants may be entering the country to attack coalition forces.

For instance, Sunday, coalition forces killed six insurgents and detained 54 suspects in raids in the town of Qaim, targeting terror group, al-Qaeda.

While there was no word of casualties from the Anbar operation, insurgent violence was known to have killed nine US service members in Iraq at the weekend, raising the death toll to more than 300 from insurgent attacks in Iraq since April 28, when a new Iraqi cabinet was approved by parliament.

At least 1,600 members of the US military have now died since the beginning of the Iraq war in March 2003.

Also Monday, a wave of attacks by insurgents continued in Baghdad. Among them, a suicide car bomb attack killed three Iraqis, at least two of them police officers.

Suicide drivers are invariably foreign fighters. Officers in Baghdad said they knew of no case in which a suicide attacker turned out to have been an Iraqi. The number of car bomb attacks jumped from 64 in February to 135 in April. The proportion of such attacks involving a suicide driver also soared, from about 25 percent to just over 50 percent.

Overall, the rate of attacks against US, coalition and Iraqi forces and civilians has climbed from about 30 to 40 a day in February and March to an average of about 70 a day now.ASSOCIATED PRESS, THE WASHINGTON POST