A US drone strike targeting a militant compound killed six rebels in Pakistan's tribal region of North Waziristan near the Afghan border on Tuesday, security officials said.

The strike took place in Miranshah Bazaar, part of the town of Miranshah, in the troubled North Waziristan region, known as a strong bastion of Taliban and Al-Qaeda linked militants.

"At least six militants were killed when a US drone fired two missiles on a rebel compound in the bazaar," a security official told AFP on condition of anonymity.

He said thick smoke was seen coming out of the compound after the strike, adding the identities of those killed could not be immediately verified.

Another security official also confirmed the strike and rise in the death toll, given as three earlier.

Covert CIA drones are the chief US weapon against Taliban and Al-Qaeda militants who use Pakistan's lawless tribal areas as launch pads for attacking US troops in Afghanistan and plotting attacks on the West.

Under President Barack Obama, the United States has drastically stepped up drone strikes in Pakistan but it refuses to discuss them publicly. The strikes have boosted anti-US sentiments in the country.

More than 60 US drone strikes have been reported in Pakistan so far this year, and dozens since Navy SEALs killed Al-Qaeda leader Osama bin Laden in the garrison city of Abbottabad, close to the capital Islamabad, on May 2.

The raid humiliated Pakistan but is thought to have contributed to debate within the military about the merits of traditional support for jihadi groups.

Visiting Islamabad last month, US Secretary of State Hillary Clinton called on Pakistan to take action within "days and weeks" on dismantling Afghan militant havens and encouraging the Taliban into peace talks.

But although Pakistan recognised it could do more in clamping down on Afghan insurgents, it offered no details on how, and commanders are unwilling to launch a sweeping offensive in North Waziristan, base of the Haqqani Taliban faction.

Relations between Pakistan and the United States deteriorated sharply this year over the bin Laden raid in May and again over accusations that Pakistani intelligence was involved in September's siege of the US embassy in Kabul.

The United States blames the Haqqanis for fuelling the 10-year insurgency in Afghanistan, attacking US-led NATO troops and working to destabilise the Western-backed government of Afghan President Hamid Karzai.

The tense partnership between Pakistan and the United States in the war on terror took a further battering last month, with Washington demanding that Islamabad take action against the Haqqani network and cut ties to the group.

The Pakistani military says it is too over-stretched fighting local Taliban to acquiesce to American demands to launch an offensive against the Haqqanis, a battle that not all observers think the Pakistani military would win.