A military spokesman in Swat also confirmed the incident and said security forces had foiled a suicide attack on Tuesday and destroyed a explosives-laden vehicle in the area.

Swat battleground

For the past year, security forces have been fighting loyalists of pro-Taliban leader Mullah Fazlullah, who has led a violent campaign to impose Taliban-style law in Swat, a mountain valley once popular with tourists.

Pakistan also launched a military offensive in August against fighters in the nearby Bajaur tribal region, bordering Afghanistan.

Pakistani tribal lands are regarded as safe havens for al-Qaeda and pro-Taliban fighters.

Violence has surged in these regions since 2007, and the number of US missile strikes by pilotless drone aircraft against fighter targets have increased in recent months.