KABUL:The U.S. military faced more criticism in Afghanistan on Monday as a charity accused American soldiers of storming through a provincial hospital, breaking down doors and tying up staff and visitors in a hunt for insurgents.

Critics say such heavy-handed tactics violate international principles and threaten to undermine support for the war against the Taliban. The American military said it was investigating the allegation, which comes on the heels of a furor over disputed reports that up to 70 Afghan civilians died in a NATO airstrike in the country's north last week.

Civilian deaths and intrusive searches have bred resentment among the Afghan population nearly eight years after the U.S.-led coalition invaded to oust the Taliban's hard-line Islamist regime, which was sheltering al-Qaida terrorist leaders.

On Monday, the Swedish Committee for Afghanistan said the U.S. Army's 10th Mountain Division forced their way into the charity's hospital to look for insurgents in Wardak province, about 40 miles (60 kilometers) southwest of Kabul.

"This is a clear violation of internationally recognized rules and principles," said Anders Fange, the charity's country director. No one was harmed in the raid, but Fange said it violated an agreement between NATO forces and aid groups working in the area.

U.S. military spokeswoman Lt. Cmdr. Christine Sidenstricker confirmed that the hospital was searched last week but had no other details. She said the military was looking into the incident.

"We are investigating, and we take allegations like this seriously," she said. "Complaints like this are rare."

Fange said U.S. troops kicked in doors, tied up four hospital guards and two people visiting hospitalized relatives, and forced patients out of beds during their search late Wednesday night.

They also barged into the women's wards, he said, adding that strange men entering rooms where women are in beds is a serious insult to the local Muslim culture and word of it could turn the community against international troops.

When they left two hours later, the soldiers ordered hospital staff to inform coalition forces if any wounded insurgents were admitted, and the military would decide if they could be treated, he said.

The staff refused. Fange said informing on patients would be an ethical breach, put the staff at risk and make the hospital a target. He demanded guarantees the military would not enter hospitals without permission in future.

"If the international military forces are not respecting the sanctity of health facilities, then there is no reason for the Taliban to do it either," he said. "Then these clinics and hospitals would become military targets."

While the search operation may have sparked outrage and goes against common practice, it's not clear whether it broke any international rules of war. International humanitarian law, which includes the Geneva Conventions, requires that civilian hospitals be respected and also protects medical personal and the sick and wounded from combat operations. However, it does not specifically address search operations.

Violence has surged across much of Afghanistan since President Barack Obama ordered 21,000 more U.S. troops to the country this year. Two Canadian troops were killed Sunday when their patrol hit a roadside bomb near Kandahar, Canada's Defence Ministry said. A third service member died of wounds sustained in a separate gunbattle with insurgents in southern Afghanistan, NATO said without giving a nationality.

NATO was also investigating last week's U.S. airstrike in northern Kunduz province. The strike came despite new rules for foreign forces limiting use of airpower to avoid civilian casualties. An Afghan human rights group said Monday the strike on two hijacked fuel tankers may have killed as many as 70 villagers, but a spokesman for the provincial government said all but five of the dead were insurgents.

The increasingly violent Taliban insurgency has killed more civilians in bombings and other attacks than international forces have. On Monday, the government said three militant rockets landed overnight in the capital, Kabul, hitting a house and killing three people. In central Uruzgan province, a remote-controlled bomb targeting a police vehicle exploded in a busy market, killing two children and wounding 16 other people, according to local police official Gulab Khan.

A United Nations report in July said the number of civilians killed in conflict in Afghanistan has jumped 24 percent this year, with bombings by insurgents and airstrikes by international forces the biggest killers. The report said 1,013 civilians were killed in the first half of 2009, 59 percent in insurgent attacks and 30.5 percent by foreign and Afghan government forces. The rest were undetermined.