US drone strikes killed a prominent warlord who had sent insurgents to fight in Afghanistan as well as nine other militants in South Waziridan, 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. He is one of the highest-profile drone victims in recent years.

Officials said a US drone fired two missiles at his vehicle in the Sar Kanda area of Birmil in South Waziristan, and five of his loyalists including two senior deputies were also killed.

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

The official 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 along the Afghan border.

Another official said Nazir and his fighters were targeted as they prepared to swap vehicles when their pick-up encountered a mechanical fault.

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

Local residents later 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 suspected militants on Thursday but their identities were not immediately known, other security officials said.

Although Nazir's fighters have long been targeted by US drone strikes, he reached a peace deal with Washington's 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.

Nazir was understood to be close to the 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.

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.

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 his death could unleash chaos given that Nazir 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.