A US drone aircraft killed at least 45 Pakistani Taliban militants in south Waziristan yesterday when it fired missiles at the funeral of an insurgent commander killed earlier in the day, Pakistani intelligence officials said.

"Three missiles were fired by drones as people were dispersing after offering funeral prayers for Niaz Wali," one intelligence official said, referring to a Taliban commander who was one of six militants killed in an earlier drone attack.

The army had no information on the attack on the funeral in the remote area under the control of Baitullah Mehsud, the country's enemy number one, a military official said.

One local security official, who could not be identified as he was not authorised to speak to media, said that more than 60 had died of whom "half are civilians". Funerals of Taliban are attended by local villagers, not just militants.

Waziristan, which borders Afghanistan, is part of Pakistan's lawless tribal area, where US forces have mounted about 60 drone attacks against suspected militants since early last year.

But bombing a funeral is unusual and may be unprecedented. Local media reports said a local commander named Sangeen, originally from Afghanistan, was among the dead.

Mehsud, an al-Qaida ally accused of plotting the assassination of former prime minister Benazir Bhutto in 2007, had been in the area but was not hurt, a Taliban official said.

The US has offered a reward of $5m for information leading to Mehsud's location or arrest.

The attacks came as Pakistan's efforts to tame the burgeoning Taliban movement in the west of the country suffered a blow when a rival of Mehsud was shot dead, apparently by one of his own guards.

Qari Zainuddin, who had repeatedly criticised the Pakistani Taliban's chief for targeting civilians, was shot in his office in the town of Dera Ismail Khan. Baz Mohammad, one of Zainuddin's aides who was wounded in the attack, said a guard barged into a room at the leader's compound after morning prayers and opened fire. Mohammad accused Mehsud of being behind the attack and vowed to avenge the death.

"It was definitely Baitullah's man who infiltrated our ranks, and he has done his job," Mohammad told AP.

The guard, who is thought to have insinuated himself into Zainuddin's circle about four months ago, fled in a waiting car after the attack. Mehsud, described as the mastermind behind much of the terrorist activity in Pakistan, has yet to comment on the killing.

Zainuddin was estimated to have about 3,000 armed followers in Dera Ismail Khan and nearby Tank. Earlier this month, he denounced Mehsud for the killing of civilians in recent attacks, which were apparently launched in retaliation for the army offensive in the Swat valley.

The country's armed forces are driving militants from the valley and have been pounding Mehsud's strongholds in the South Waziristan tribal region, near Afghanistan, in apparent preparation for a big offensive against the warlord.

While some saw the killing as a sign of a schism within the Pakistani Taliban, other analysts argued that Zainuddin's death removes from the scene an important threat to Mehsud. Some believe Mehsud feared Zainuddin more than the Pakistan army because he was an opponent from within, with intimate knowledge of his methods and personnel.

Zainuddin could have rallied the Mehsud tribe, perhaps the only way of eliminating Baitullah Mehsud and his network. For the first time since Mehsud became leader of the main group of the Pakistani Taliban four years ago, Zainuddin's bold stance had given others in the Mehsud clan the courage to speak up against his vicious reign, which broke all tribal traditions.

A tribal leader from South Waziristan, too scared to be named, said: "The message from Baitullah Mehsud is that who-ever wants to come openly against me will meet the same fate."

Zainuddin, 30, was protected by two dozen armed guards at his compound, but the security was not as strong as might be expected for someone who had taken on so violent an enemy. The danger was obvious. Mehsud had demonstrated his ruthlessness by killing hundreds of the Mehsud tribe's traditional elders - who might have led resistance - as he came to power.