U.S. and Iraqi forces in the volatile western province of Anbar have seized thousands of pounds of explosives and arrested dozens of suspected insurgents in a three-day sweep that has encountered little resistance and received widespread cooperation from local residents, military officials said Thursday.

The thrust by about 1,000 U.S. Marines, soldiers and sailors and 100 Iraqi soldiers, called Operation Sword, centered on towns along the Euphrates River about 90 miles west of Baghdad. Marine spokesmen have said the operation, like other recent sweeps farther west, is aimed at driving insurgents out of towns and disrupting their ability to move fighters, weapons and supplies from neighboring Syria into western Iraq and other parts of the country.

"Since the combined force of Marines and soldiers entered the city of Hit on Tuesday, there has been no significant resistance or opposition," said Lt. Col. Christopher C. Starling, operations officer with the Marines' Regimental Combat Team 2. "The people have been overwhelmingly receptive and have assisted coalition and Iraqi solders in locating roadside bombs and weapons caches."

A Marine statement said there had been no fighting reported Thursday, no buildings destroyed and no airstrikes conducted.

The combined American and Iraqi forces have searched hundreds of homes and businesses, according to witnesses, some of whom expressed gratitude for the operation.

Capt. Hussein Abbas of the Iraqi army said that about two tons of explosives had been confiscated in Hit and that 45 suspects had been arrested, including some from Saudi Arabia, Jordan and Syria.

Iraqi and U.S. officials say prospective insurgents from Europe, Africa and Asia have been undergoing training in Syria and then crossing the border into Iraq, all with the consent of the Syrian government.

In Baghdad on Thursday, the U.S. military's chief spokesman in Iraq, Air Force Brig. Gen. Donald Alston, said: "These borders are porous, and it requires more than just posting guards on the Iraqi side of the border. It requires support from Iraq's neighbors, and the Iraqi government has petitioned all of its neighbors to do more to secure their borders."

Alston told reporters the military estimated that foreigners accounted for roughly 5 percent of an insurgency believed to number between 15,000 and 20,000. But Alston said many of those fighters were "folks that don't choose to fight every day." The core of the insurgent movement measured "more in the hundreds," he said.

The insurgents -- Iraqis and foreigners alike -- are overwhelmingly Sunni Muslim Arabs. Iraqi leaders have repeatedly emphasized the importance of undercutting the insurgency by drawing Iraqi Sunnis into a political process that is so far dominated by Shiite Muslims and ethnic Kurds, who also are Sunnis.

On Wednesday, a former Iraqi electricity minister, Aiham Alsammarae, announced that he had formed a Sunni political organization whose members would include some Iraqis with links to insurgent groups.

On Thursday, however, three insurgent groups -- the Ansar al-Sunna Army, the Mujaheddin Army and the Islamic Army in Iraq -- distributed a statement at a mosque in Hit saying they were not involved with Alsammarae's organization and had not taken part in talks with U.S. or Iraqi officials. The statement threatened Alsammarae with death.

"All the resistance groups decided to shed the blood of Aiham Alsammarae because he claimed that he is the mouthpiece of the resistance," the statement said. "We will not talk to the occupation forces except with one language, which is the language of weapons. We promise to continue on our path and will negotiate with the occupier when we see their vehicles leave Iraq."