President Hamid Karzai condemned a U.S. airstrike Thursday that Afghan officials said killed 10 border policemen. Sixteen other people died in violence around the country, including an American soldier slain by a Soviet-era land mine.

The U.S. military said it was investigating the airstrike in southeastern Afghanistan, but believed it had struck insurgents fleeing the scene of an attack on U.S. and Afghan troops.

Two suicide bombers targeted U.S. and NATO troops, seriously wounding one American soldier and killing an Afghan civilian. A purported spokesman for the Taliban said it would launch more such attacks in the future.

Afghanistan is going through its worst period of violence since the U.S.-led invasion that ousted the hard-line Taliban regime in late 2001 for hosting Usama bin Laden.

CountryWatch: Afghanistan

Karzai said he was "shocked and angered" by the airstrike in southeastern Paktika province.

"I have repeatedly asked the coalition forces to take maximum caution while carrying out operations and I want that incidents like this must not be repeated," he said in a statement.

Gen. Abdul Rahman, Afghanistan's deputy chief of border police, said a coalition airplane killed 10 policemen in two trucks. No one survived the strike.

The U.S. military released a statement saying it was looking into the report but it believed an aircraft had destroyed two trucks that soldiers on the ground said were involved in an insurgent attack on a U.S.-Afghan patrol. An Afghan policeman was killed and coalition vehicle damaged in that clash.

Karzai has urged restraint on the part of coalition forces operating in areas where civilians live. In April, clashes pitting U.S., Canadian and British troops against insurgents left 13 Afghan civilians dead.

In Paktika province on Wednesday, a U.S. military vehicle hit a Soviet-era land mine, killing one soldier, the military said, ruling out enemy action.

On Thursday, a suicide bomber drove an explosives-packed car into a joint U.S.-Afghan army convoy on the main Kandahar-Kabul highway in Kandahar province, seriously wounding one U.S. soldier, officials said.

A purported Taliban spokesman claimed responsibility for the attack and said the bomber was Afghan.

Militants will continue with "suicide bombings, guerrilla warfare and ambushes" against the U.S. and their allies in Afghanistan, said Qari Yousaf Ahmadi, a self-described Taliban spokesman who contacted The Associated Press by telephone.

In nearby Uruzgan province, another suicide bomber targeting a NATO patrol instead killed one civilian and wounded six others, a NATO spokesman said.

The Afghan Interior Ministry said eight police were wounded, four seriously, in an attack by a bomber wearing explosives strapped to his body.

The coalition also said U.S. soldiers killed eight militants during a firefight near eastern Kunar province's capital of Asadabad.

Meanwhile, suspected Taliban militants released 17 health workers unharmed, including doctors and nurse, who had been abducted earlier in the day in southern Kandahar province, said NATO spokesman Maj. Quentin Innis.

Taliban spokesman Ahmadi said insurgents commandeered the workers' minivan but did not kidnap the passengers, who he claimed fled into nearby villages.

In eastern Paktiya province, the provincial police chief said an air strike in mountainous Mutrekh village killed three people and wounded four late Tuesday. The U.S. military denied any coalition bombing activity in the area.