Since then, the sweep, dubbed Operation Matador, has seen some of the heaviest fighting since U.S. forces took control of Al-Fallujah in November.
U.S. General James Conway told reporters in Washington yesterday that three Marines had been killed in western Iraq and fewer than 20 wounded. News reports say that some 110 insurgents have also been killed in the fighting.
Conway said that the operation is intended to rout insurgents from new strongholds they have established in western Al-Anbar Governorate since being pushed out of Al-Fallujah in the east of the majority Sunni province some six months ago.
Recently, I think, it is fair to say that commanders have evaluated that the center of resistance in Al-Anbar [province] has moved further west since the fall of Fallujah and is now in the Ramadi-Hit corridor, extending westward, as opposed to Ramadi-Fallujah," Conway said.
Intense fighting has taken place in a string of towns toward the Syrian border at the western edge of the province. The area is part of the insurgents' smuggling route for weapons, supplies, and foreign fighters believed to be arriving via Syria. The region is also thought to be a safe haven for Al-Qaeda's leader in Iraq, Abu Mus'ab al-Zarqawi.
U.S. forces have encountered well-organized resistance on both sides of the Euphrates River, which runs through the area.
In one measure of the scale of the offensive, U.S. forces completed construction of a pontoon bridge across the Euphrates on 9 May to bring heavy armored vehicles over to the south bank. Previously, there had been no easy way to deploy armored vehicles throughout the area.
Conway said that the insurgents are well trained and equipped and have put up fierce resistance. "There are reports that these people [insurgents] are in uniforms, in some cases are wearing protective vests, and there is some suspicion that their training exceeds that of what we have seen with other engagements further east," he said.
Asked if he was surprised by the level of resistance, Conway answered: "I don't think we are surprised. We know, again, that this is a determined enemy, that he has the skill and the ordnance, the weapons, to be able to resist fiercely, as we are seeing here. So, it should not be a surprise to us when that happens."
News reports say that fighting has taken place in the towns of Obeidi, Al-Rommanah, Al-Karabilah, and Al-Qa'im as insurgents are reported to have fired at Marines from rooftop positions and bunkers.
Analysts say the level of fighting raises new questions about how much progress Washington and Baghdad are making in the now two-year-old effort to quell the insurgency.
U.S. commanders had hoped that routing the insurgents from their earlier stronghold in Al-Fallujah would knock the insurgency off balance. In that operation, some 1,500 insurgents were killed and another 1,500 captured.
But the insurgents have since shown themselves to be highly flexible in moving their operations to other parts of central Iraq.
Jeremy Binnie, Middle East editor of the London-based Jane's Sentinel Security Assessments, says it is still too early to know whether the insurgency is maintaining its strength or gradually waning. He says both sides can point to successes and setbacks. "Whilst clearly the situation isn’t great for the Iraqi [government] and the U.S. military in that country, it's not going all that well for the insurgents either," he said.
But Binnie says that are signs that new political initiatives in Baghdad could divide and weaken the insurgency in ways that military pressure alone has yet to do. "There are rumors that some of the Ba'athist factions [in the insurgency] are talking to the government and there might be some possibility of an amnesty especially now that a Sunni tribal defense minister has been appointed," he said. "He might be able to bring some people in from the insurgency. And the insurgents, in some of their rhetoric and statements they publish on the Internet, seem to be concerned over the possibility of some of these factions going over."
Still, the fight both on the political and military front shows no signs of ending soon.
Yesterday, insurgents struck a direct blow against the new government by kidnapping Al-Anbar Governor Raja Nawaf Farhan al-Mahalawi. The governor, who was appointed to his post just a few days ago, was abducted while traveling to view the U.S. assault in the west of the province.
Elsewhere in Iraq, insurgent suicide bombers killed at least 50 people in Iraq today. The attacks are the latest in a wave of guerrilla violence that has killed hundreds since the new government was unveiled two weeks ago.
See also: Months Of Insurgent Activity Preceded Operation In Western Iraq
For the latest news and analysis on Iraq, see RFE/RL's webpage on "The New Iraq".