Taliban leader Mullah Omar died two years ago in Pakistan, aspokesman for Afghanistan's security services says.
Abdul Hassib Seddiqi told the BBC's Afghan Service that Mullah Omar had died of health problems at a hospital in Pakistan.
Afghanistan's government says information on his death is "credible".
The latest reports of Mullah Omar's death are being taken more seriously than previous such reports. The Taliban is expected to issue a statement soon.
Sources at the Taliban's two main councils in Quetta and Peshawar in Pakistan told the BBC they were in intensive talks to agree on a replacement for Mullah Omar.
A statement from the office of Afghanistan's President Ashraf Ghani said that it believed, "based on credible information", that Mullah Omar died in April 2013 in Pakistan.
The Afghan government, elected last year, has embarked on a peace process with the Taliban.
In its statement, the government called on "all armed opposition groups to seize the opportunity and join the peace process".
A security official in Pakistan, the country hosting the talks, told AP that the claims of Mullah Omar's death were mere "speculation", designed to destabilise the negotiations.
Pakistan's government and security services have not formally commented on the claims so far. They have always denied that Mullah Omar was in their country.
Mullah Mohammed Omar
- Taliban say he was born in 1960 in the village of Chah-i-Himmat, in Kandahar province
- Fought in resistance against Soviet occupation in 1980s, suffering a shrapnel injury to his right eye
- Forged close ties to al-Qaeda leader Osama Bin Laden
- Became "supreme leader" of Taliban movement in 1996
- US-led forces overthrew his government in 2001; US state department has a $10m bounty on him
- Earlier this year the Taliban published a biography of him saying he does not own a home and has no foreign bank account, and saying he "has a special sense of humour"