At least 10 people have died and six have been wounded after a suicide bomber rammed his vehicle into a building at a Pakistani security post in the northwestern district of Swat, an official said.

Kamal Hyder, Al Jazeera's correspondent in Islamabad, said: "A vehicle laden with explosives was used by the bomber in a compound housing a large number of security forces - a mix of paramilitary and military forces.

"As soon as that happened, the building was rocketed and shot at by fighters surrounding the area. As a result, there is the suspicion of high casualities.

"The death toll is likely to be high given that these people were taken by surprise.

"An emergency has been declared in the hospital in Swat."

US visit

The attack comes as two US senior commanders, including Mike Mullen, the chairman of the US joint chiefs of staff, visit Islamabad seeking more military operations in the northwest of Pakistan.

There have been numerous clashes and bombings in Swat Valley since Maulana Fazlullah, apro-Taliban leader, launched a campaign to enforce the Sharia (Islamic law) in the region last year.

Asif Ali Zardari, the Pakistani president, who is in London visiting Gordon Brown, the UK prime minister, pledged to combat militancy that has been plaguing the country and neighbouring Afghanistan.