A US drone attack killed at least three militants early Thursday in Pakistan's northwestern tribal region, known as a hotbed of Taliban and Al-Qaeda militants, security officials said.

The drone fired two missiles on a building in the central market of Miranshah, the main town in North Waziristan near the Afghan border, Pakistani officials said.

"A US drone fired two missiles on the first floor of a shop in the main market and at least three militants were killed," a senior official told AFP.

There has been a dramatic increase in US drone strikes in Pakistan since a NATO summit in Chicago ended last month without a deal to end a six-month blockade on NATO supplies crossing into Afghanistan.

A drone attack on June 4 killed 15 militants in North Waziristan, including senior Al-Qaeda figure Abu Yahya al-Libi.

Other security officials based in Miranshah and the northwestern Pakistani city of Peshawar confirmed the casualties in the latest attack, which comes a day after a drone killed four insurgents in the tribal region.

It was not immediately known if there were any high-value targets killed in the latest strikes.

"When the first missile hit the building, I heard cries for help and ran towards it, but militants stopped me at a distance. When they started rescue work, another missile hit," a local tribesman said about Thursday's strike.

"I eventually saw them removing three burnt bodies in a really bad shape. They were put in wooden boxes and taken away," he told AFP, requesting anonymity, adding that the attacked building was reduced to a pile of rubble.

Washington considers Pakistan's semi-autonomous northwestern tribal belt the main hub of Taliban and Al-Qaeda militants plotting attacks on the West and in Afghanistan.

Distrust over Pakistan's refusal to do more to eliminate the Islamist threat has become a major thorn in increasingly dire Pakistani-US relations.

Both sides are at loggerheads over reopening NATO supply lines that Pakistan shut in fury on November 26 when US air strikes killed 24 Pakistani soldiers.

Negotiations have snagged over costings, with American officials refusing to pay the thousands of dollars per container that Pakistan has reportedly demanded.

Islamabad initially conditioned reopening the lines on an American apology for the deaths of the 24 soldiers and an end to drone strikes, but neither is likely to happen.

From 2002 to 2011, the United States paid Pakistan $8.8 billion for its efforts to fight militancy under the CSF, but Islamabad stopped claiming the money after US troops shot dead Osama bin Laden in Pakistan in May 2011.

Pakistani authorities whipped up anti-American sentiment after the bin Laden raid and are increasingly vocal in their belief that drone strikes violate national sovereignty.

But US officials consider the attacks a vital weapon in the war against Islamist extremists, despite concerns from rights activists over civilian casualties.

UN High Commissioner for Human Rights Navi Pillay recently called for a UN investigation into US drone strikes in Pakistan, questioning their legality and saying they kill innocent civilians.

The UN human rights chief provided no statistics but called for an investigation into civilian casualties, which she said were difficult to track.

She said UN chief Ban Ki-moon had urged states to be "more transparent" about circumstances in which drones are used and take necessary precautions to ensure that the attacks involving drones comply with applicable international law.