Three
schoolgirls were among the dead while 70 people, including another 63
schoolgirls and two US soldiers, were injured in the explosion in Lower
Dir.

The US embassy said the military personnel had been training Pakistan's Frontier Corps in counter-insurgency.

Both governments deny large numbers of US troops are in Pakistan, where public opinion opposes their presence.

The
US embassy in Islamabad confirmed in a statement three American
military personnel were killed and two wounded in what it branded a
"vicious terrorist bombing".

ANALYSIS The Pakistani military and the government are both extremely sensitive about the strong US presence in their country and both appear to be saying different things to different audiences. Officially the government says it is deeply concerned about increasing numbers of US diplomatic and aid staff who have appeared in the country since US President Barack Obama declared the country to be a top foreign policy priority. The Pakistani authorities have on several occasions during the past five months arrested American officials - in Lahore and Peshawar - who were suspected of having incorrect paperwork. But unofficially the government is believed to be relying on US effort and expertise to fight the Taliban.

The statement also said the Americans had been due to attend the
inauguration of a girls' school recently renovated with US humanitarian
assistance.

Azam Tariq, a spokesman for the Pakistani Taliban,
Tehreek-e-Taliban, claimed responsibility for the attack in a statement
to AFP news agency.

Military spokesman Maj Gen Athar Abbas told
the BBC that the US personnel were attached to the Frontier Corps as
military trainers.

Pakistan's Frontier Corps is a paramilitary
force responsible for operations against militants in the volatile
north-west, near the Afghan border.

The US soldiers were said
to have been travelling in a convoy, along with Pakistani troops, that
was heading to the inauguration of a newly built girls' school in
Maidan, an area of Lower Dir district in Pukhtunkwa.

The bomb - which police said was activated by remote
control - occurred near a different school in Koto, a heavily populated
village along the route.

The impact flattened much of the Koto Girls' High School, leaving pupils crying for help from under the rubble.

'Highly embarrassing'

At
least three of the dead were schoolgirls, police said, adding that
security guards and three local journalists were also among the
wounded.

The Taliban has often targeted girls' schools in recent years

News that three US soldiers were killed will be highly embarrassing
for the Pakistani government, which is acutely aware of the
unpopularity of its close ties to Washington. 

Critics accuse Pakistani President Asif Ali
Zardari of turning a blind eye to repeated American drone attacks in
the north-west, which have killed more than 600 people during the past
year, our correspondent says.

The US has argued in the past that its soldiers are in Pakistan to provide security for US citizens. 

Last
year, the Pakistani army carried out a major offensive to drive Taliban
insurgents out of Lower Dir and the neighbouring districts of Swat and
Buner.

But the Taliban are still present in remote areas and
the latest attack shows that the militants remain a powerful force in
the region. 

Prime Minister Yousuf Raza Gilani also condemned the attack and ordered an investigation.

The Taliban has frequently targeted girls' schools in recent years, burning several to the ground. Many are now being rebuilt.