A suspected US drone strike has killed at least five fighters at a suspected training ground in Pakistan's northwestern border region, Pakistani intelligence officials have said.

Up to two missiles fired from the unmanned aircraft struck a building near the town of Mir Ali in North Waziristan, close to the border with Afghanistan, officials said on Sunday.

The area is known to be a base for Taliban and al-Qaeda fighters, they said.

The US has stepped up its operations in the region since a suicide bomber killed seven CIA employees in Afghanistan late last year.

A barrage of US drone strikes hit Pakistan's northwest tribal belt in January, most concentrated around main North Waziristan town of Miranshah.

On February 2, US drones fired a large volley of missiles at an extremist stronghold in North Waziristan, killing at least 16 militants, but there had been a lull in such raids since then.

Speaking to the AFP news agency a local government official confirmed Sunday's strike, saying the targeted compound about 25km east of Miranshah was used for training fighters.

The attack came as US forces across the border in Afghanistan spearhead one of Nato's biggest offensives against the Taliban – a move seen as key early test of the revised US strategy in the country.

As well as taking on the Taliban in Afghanistan, the US is keen to eradicate their sanctuaries in ethnic Pashtun tribal lands on the Pakistani side of the border.

Pakistan has objected to the US use of drone strikes in its territory, saying they are a violation of its sovereignty and fuel anti-US feeling in turn complicating Pakistan's own efforts to battle militancy.