Three American soldiers were among the eight people killed in a roadside bomb attack in northwest Pakistan on Wednesday, the army said.

The American soldiers were military trainers for the Pakistani Frontier Corps, it said. The U.S. embassy in Pakistan said it is investigating the reports and will soon issue a statement.

A Pakistani soldier and four school girls were also killed in the attack near a school at Koto area in Tehsil Balambat of Lower Dir district in North West Frontier Province, officials said.

Up to 60 people, most of them school children, were injured in the attack. The injured were taken to hospitals in Timargarah and Mingora. Several local journalists were also among the injured persons, police said. The blast also caused damage to the school building and nearby houses.

According to District Police Officer (DPO) Lower Dir, Mumtaz Zarin, the bomb was planted to target the convoy of security personnel and foreign guests, who were going to Midan in Dir to attend a ceremony of reopening of school.

No group claimed responsibility for the attack. The authorities said that Taliban militants are behind the attack.

The security forces conducted a major operation against the Taliban militants in Dir district in 2009. Local people had also formed "lashkar" (army) to fight the militants in Dir.

Dir district has seen attacks on security forces in recent months.