MIRANSHAH: A US drone attack killed four insurgents on Wednesday in Pakistan's northwestern tribal region, known as a hotbed of Taliban and al Qaeda militants, security officials said.

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 from Pakistan.

A drone attack killed 15 militants in North Waziristan on June 4. The dead included senior al Qaeda figure Abu Yahya al-Libi, according to US officials.

It was not immediately known if there was any high-value targets killed in the latest strike, which again took place in North Waziristan.

“The drone fired two missiles on a vehicle,” a security official said. “The death toll has gone up to four,” he added. Previously he said three militants had been killed.

The vehicle was hit in Isha village, about 10 kilometres east of Miranshah, two other security officials said. The vehicle caught fire after the attack, they said. Miranshah is the main town in North Waziristan.

Nine drone strikes have been reported in Pakistan since May 23 and the June 4 strike was the deadliest since 18 Pakistani Taliban were reported killed on November 16, 2011.

North Waziristan is Pakistan's premier bastion of militants and where Islamabad has rejected US pressure to wage a major ground offensive against militants active in the 10-year war against US troops in Afghanistan.

Wednesday's attack came after the United States withdrew negotiators from Pakistan when talks failed to reopen Nato supply routes.

The move signalled a further strain in troubled Pakistani-US relations and followed harsh criticism last week from US Defense Secretary Leon Panetta that saw Pakistan's army chief refuse to meet a senior Pentagon official.

The negotiators had been in Pakistan for about six weeks and US officials believed they were close to a deal with Islamabad to lift the blockade.

Pakistan shut its border to Nato supply convoys on November 26 after a botched US air strike killed 24 Pakistani soldiers.

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 militant threat has become a major thorn in increasingly dire Pakistani-US relations.

Pakistani authorities whipped up anti-American sentiment after a covert US raid killed Osama bin Laden 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 extremists, despite concerns from rights activists over civilian casualties.