US drone strikes killed a prominent warlord who sent insurgents to fight NATO troops in Afghanistan along with nine other militants in Pakistan's tribal belt, local officials said Thursday.

Mullah Nazir was the main militant commander in South Waziristan, part of the tribal zone where militants linked to the Taliban and Al-Qaeda have bases on the Afghan border. He is one of the highest-profile drone victims in recent years.

Pakistani officials said an unmanned US aircraft fired two missiles at his vehicle in the Sar Kanda area of Birmil in South Waziristan, killing Nazir and five of his loyalists, including two senior deputies.

"Mullah Nazir and five associates died on the spot," one of the officials told AFP on condition of anonymity.

He said the attack happened at 10:35 pm on Wednesday (1735 GMT) but that it took time to confirm the reports from such a far-flung and mountainous area.

Another Pakistani official said Nazir, believed to have been in his late 30s, was targeted as he prepared to swap vehicles after his pick-up developed a mechanical fault.

Two of his influential deputies, Atta Ullah and Rafey Khan, were among those killed, the official added.

Local residents told AFP that funeral prayers were said for Nazir and his associates around 10 kilometres (six miles) west of Wana, the main town in South Waziristan, and markets and shops closed.

In the neighbouring district of North Waziristan, two more missiles fired from a US drone killed four other militants on Thursday but their identities were not immediately known, other Pakistani security officials said.

Nazir's fighters have long been targeted by US drone strikes.

He was understood to be close to the Al-Qaeda-linked Haqqani network, a faction of the Afghan Taliban blamed for some of the most high-profile attacks in Kabul and elsewhere in Afghanistan in recent years.

"This is someone who has a great deal of blood on his hands," said US Pentagon spokesman George Little. "This would be a major development."

Nazir reached a peace deal with US ally Islamabad in 2007 and had testy relations with the Pakistani Taliban, who are fighting a domestic insurgency.

He was wounded in a suicide attack in South Waziristan on November 29 and had survived previous attempts on his life.

-- Analysts divided on impact --

Pakistani security officials were locked in talks to assess the impact of Nazir's death, which one official told AFP would benefit Pakistani Taliban who want to move into South Waziristan.

"There will be a setback in a way. He was one of those who were keeping his area under effective control and preventing the Tehreek-e-Taliban Pakistan from operating there. So it will make a difference," the official said.

Analysts were divided on the impact that his death would have on Pakistan and on the US-led war against an 11-year insurgency in neighbouring Afghanistan.

A Pakistani author and expert on the tribal belt, Imtiaz Gul, suggested there would be little fallout for Pakistan, which is trying to assist efforts by the Western-backed Kabul government to broker a peace deal.

"The Americans and Afghans suspected Mullah Nazir of sheltering and hosting Arab Al-Qaeda operatives," Gul told AFP.

"They (the US and its coalition partners) want to eliminate whatever elements are left in the border regions to minimise the threat that Arab Al-Qaeda poses to US forces in Afghanistan."

But Saifullah Khan Mehsud, executive director of the FATA Research Center, said Nazir's death could unleash chaos given that he tried to contain the Pakistani Taliban and keep Wazir tribes and militant groups united.

Nazir had sporadic alliances with Pakistan's umbrella Tehreek-e-Taliban faction, which is dominated by members of the rival Mehsud tribe.

"If he is dead then it is a big problem for the Wazir tribe, it is a big problem for the Pakistani army," said the Research Center executive director.

"And I don't know what the US was thinking when they decided to hit him, because why would you make things difficult for your most important ally in the region? That would create chaos in that region," he added.

Nazir was an enemy of Uzbek militants in the Islamic Movement of Uzbekistan and was in 2007 congratulated by Pakistan for expelling Uzbek and other foreign Al-Qaeda-linked militants from South Waziristan.

In April 2007 he gave a rare press conference at which he said he had never met Osama bin Laden but would protect him if asked.

Covert US drone strikes are publicly criticised by the Pakistani government as a violation of sovereignty, but American officials believe they are a vital weapon in the war against Islamist militants.