At least five militants were killed in two separate US drone strikes early Wednesday in a northwest tribal district where Pakistan has this week launched a major military offensive.

Local security officials said six missiles hit three compounds in Dargah Mandi village in North Waziristan, around 10 kilometres (six miles) west of the main town of Miranshah in an area considered a stronghold for the Al-Qaeda-linked Haqqani network.

"US drones fired six missiles which hit three separate compounds in two villages, at least five militants have been killed," a local security official in Miranshah told AFP.

The identities of those killed in the strikes were yet not clear, the official said.

The attacks took place just minutes apart. Two drones fired four missiles in the first strike, then a third drone fired a further two missiles in the second attack, the official said.

Another senior security official confirmed the strike and told AFP that a vehicle parked in one compound was also hit, adding the death toll could rise.

Washington reportedly suspended its drone programme in December to give Islamabad time to pursue a dialogue process with the Pakistani Tehreek-e-Taliban (TTP) aimed at ending a seven-year insurgency that has claimed thousands of lives.

However the nascent peace process was shattered when the Taliban launched an attack on the airport in Karachi on June 9 that left dozens dead.

The US resumed the programme last week, days after the Karachi attack, with two strikes in the same village of Dargah Mandi, killing at least 16 militants.

Islamabad condemned those strikes, despite suspicions the two countries coordinated in the aftermath of the Taliban siege, branding them "a violation of Pakistan's sovereignty and territorial integrity" in a foreign office statement.

Leaked documents have shown deep cooperation over drone attacks in the past, but they remain controversial, with critics charging they cause many civilian casualties.

Some 2,171 people have been killed in drone attacks since August 2008, according to an AFP tally.

Pakistan's army launched its long-awaited military offensive -- a standing demand of the United States -- on Sunday, a week after the Karachi attack, deploying troops, tanks and jets to the area in the crackdown on the Taliban and other militants.

Prime Minister Nawaz Sharif has urged Afghanistan's leader Hamid Karzai to help seal the border in the mountainous tribal area between the two countries to stop insurgents escaping the offensive.

Air strikes early Tuesday targeted three Taliban strongholds in the town of Mir Ali in the North Waziristan region, killing 25 of the militants, according to official statements, raising the total insurgent death toll to 201.

The figure could not be independently confirmed.