The leader of the Pakistani Taliban, Hakimullah Mehsud, has been killed in a drone strike, a high-ranking Taliban official has told the BBC.
The strike targeted a vehicle used by Mehsud with four missiles in the north-western region of North Waziristan.
Four other people were killed in the strike, including two of Mehsud's bodyguards, intelligence sources say.
Several previous claims of his death, made by US and Pakistani intelligence sources, have proven untrue.
Pakistan's government has issued a statement strongly condemning the drone attack, saying such strikes were a "violation of Pakistan's sovereignty and territorial integrity".
Friday's strike targeted Mehsud's vehicle in the Dande Darpakhel, some 5km (3miles) north of the region's main town, Miranshah.
A senior US intelligence official told the Associated Press that the US received positive confirmation on Friday morning that he had been killed.
However, a spokesperson for the US National Security Council said that "we are not in a position to confirm those reports, but if true, this would be serious loss for the... Taliban".
BBC diplomatic correspondent James Robbins says that however weakened the Taliban may be by this loss, they will fight on under a new leader.
Hakimullah Mehsud had come to prominence in 2007 as a commander under the militant group's founder Baitullah Mehsud, with the capture of 300 Pakistani soldiers adding to his prestige among the militants.
In January 2010 he gained further notoriety when he appeared in a video alongside a Jordanian who is said to have blown himself up, killing seven CIA agents in Afghanistan to avenge Baitullah Mehsud's death.
Hakimullah Mehsud had a $5m FBI bounty on his head and was thought to be responsible for the deaths of thousands of people.
Mehsud became leader of the Pakistani Taliban in 2009, aged 30, after Baitullah Mehsud died in a US drone strike at his father-in-law's residence in South Waziristan.
The strike against Baitullah Mehsud reportedly came after repeated complaints by Pakistani officials that the Americans were not hitting militant groups who attacked targets in Pakistan.
His second-in-command, Waliur Rehman, died in a drone strike in May.
The attack targeting him comes on the same day that the Pakistani government announced it was about to send a delegation to North Waziristan to try to get peace negotiations with the Taliban under way.
Pakistani Prime Minister Nawaz Sharif had pledged to talk with the Taliban to try to end its campaign of violence, which has left thousands dead in bombings and shootings across the country.
In a rare interview with the BBC two weeks ago, Mehsud said he was open to "serious talks" with the government but said he had not yet been approached.
Mehsud denied carrying out recent deadly attacks in public places, saying his targets were "America and its friends".
He had loose control over more than 30 militant groups in Pakistan's tribal areas.
The BBC's M Ilyas Khan in Islamabad says that Khan Said Sajna is one of those now tipped to become the new leader of the Pakistani Taliban.