At least nine Afghan soldiers were killed when rebels ambushed their vehicle in Helmand province on Thursday, said Haji Wali Mohammed, a spokesman for the governor.

"We lost contact with the Afghan soldiers late Thursday, and their bodies were found today," he said, adding that authorities would hunt down and arrest the "terrorists" who carried out the attack.

Taliban rebels claimed responsibility for the ambush in the district of Chakul.

"Yes, the Taliban did this and we will launch more attacks against government and coalition forces," Mullah Latif Hakimi, who often speaks for the Taliban, told The Associated Press by telephone.

In neighboring Kandahar, an American soldiers was shot and wounded when he and his unit came under small-arms fire while investigating a roadside bomb Thursday, the U.S. military said in a statement.

Meanwhile, rebels ambushed an Afghan patrol in Khost province, near the border with Pakistan, injuring five soldiers. Afghan and U.S. forces fired back, killing three Taliban suspects.

Two U.S. helicopters sent to survey the area hours later were attacked from the ground with small-arms fire. One helicopter fired back, killing seven more suspected insurgents, the U.S. military said.

The series of attacks follows a period of relative calm in Afghanistan amid rising hopes the insurgency was faltering. Taliban spokesmen have said attacks were down only because of the harsh winter and that they would resume once the weather improved. The three attacks — all carried out Thursday — appeared to make good on that claim.

Taliban rebels have mounted a stubborn insurgency across southern and eastern Afghanistan since U.S. forces ousted the Taliban government in late 2001 for harboring Osama bin Laden and his supporters.

U.S. Maj. Gen. Eric Olson said Friday that Taliban and al-Qaida insurgents remain a grave threat to Afghanistan, and warned against cutting the strength of the U.S.-led coalition so long as neither Afghan nor NATO forces are ready to fill the breach.

"The U.S. presence at the core of the coalition has been critical to success of the overall coalition effort," Olson, the No. 2 U.S. commander in Afghanistan, told The Associated Press.

Only about 1,000 of the 18,000 coalition troops are non-Americans, including a contingent of Egyptian medics, teams of French and Norwegian special forces, and a Romanian battalion in the southern city of Kandahar.

Olson, who spoke to the AP after visiting troops at three remote bases near the mountainous Pakistani border, said the operation is very taxing and there will be pressure to draw down forces while handing over more responsibility to what is now a 9,000-strong NATO security force.

"My fear is that will happen too fast, that the draw down will outrun the expansion or the compensation of NATO expansion," said Olson.

Olson reiterated that the trail of al-Qaida leader Osama bin Laden had "gone cold," but he said U.S. forces were keeping up their search and he did not anticipate any letup in that part of their mission.

"There are no specific leads to bin Laden right now, but we collectively are just as determined to continue to hunt him," he said.