Obeidi, Iraq ? The U.S. military declared Saturday that its weeklong offensive near the Syrian border had “neutralized” an insurgent sanctuary there. But less than 24 hours earlier, fighters armed with machine guns and rocket-propelled grenades swaggered through the desert town where the campaign began.

U.S. forces killed more than 125 insurgents, injured many more and detained 39 “of intelligence value” during the campaign aimed at followers of Iraq’s most wanted terrorist Abu Musab al-Zarqawi, the military said in a statement.

Nine U.S. Marines were killed and 40 injured during the offensive known as Operation Matador — one of the largest American campaigns since militants were driven from Fallujah six months ago. The number of civilian casualties was not immediately known.

American troops, backed by warplanes and helicopter gunships, swept through desert outposts along ancient smuggling routes, believed to be staging areas for foreign fighters who slip over the border and collect weapons to launch deadly attacks in Iraq’s major cities.

Numerous weapons caches containing machine guns, mortar rounds and rockets were discovered. Six car bombs and material for making other improvised explosive devises were also found, the statement said.

The military said the operation confirmed its intelligence about a region north of the Euphrates River, including the existence of “cave complexes” used by insurgents in the nearby escarpment. It did not elaborate.

“Regimental Combat Team-2 started and ended this operation as planned, accomplished its mission and secured all objectives,” Maj. Gen. Richard Huck said in the statement. “Coalition and Iraqi Security forces will return again to this area in the future.”

But in Qaim, the town where the campaign began, masked fighters remained in plain sight Friday, setting up checkpoints and vowing to defend the town if U.S. forces return.

The U.S. assault came amid a surge of militant attacks that have killed more than 450 people in just over two weeks since Iraq’s first democratically elected government was announced.

At least 13 more Iraqis died Saturday in a series of ambushes and bombings. They included a senior Iraqi Foreign Ministry official slain in a drive-by shooting outside his Baghdad home Saturday night, police said. Three bystanders were also injured in the attack that killed Jassim Mohammed Ghani, a director general in the ministry, police Capt. Talib Thamer said.

The U.S. offensive began May 7 in Qaim, a town 200 miles northwest of Baghdad on the southern bank of the Euphrates River. American intelligence indicated insurgents had massed north of the waterway, according to reporters embedded with the assault. But as soldiers built a pontoon bridge, they started taking mortar fire from nearby Obeidi.