Taliban leader Mullah Omar died two years ago, Afghanistan's intelligence agency spokesman Haseeb Sediqi has said.
The comments come after unnamed government and militant sources told media that the one-eyed leader died two or three years ago.
"He died in a Karachi hospital in April 2013 ... under mysterious circumstances," said Mr Sediqi, the spokesman for the National Directorate of Security.
Rumours of Omar's ill-health and even death have regularly surfaced in the past. However, the latest claims, just two days before peace talks with the insurgents, mark the first such confirmation from the Afghan government.
"We can confirm that Mullah Omar died two years ago ... in Pakistan due to an illness," a separate official in Afghanistan's national unity government earlier said.
"He was buried in Zabul province [in southern Afghanistan]," said the senior official, citing Afghan intelligence sources.
The White House has said that the reports "are credible."
The insurgents have not officially confirmed the death of the supreme leader of the Taliban, who has not been seen publicly since the 2001 US-led invasion of Afghanistan that toppled the Taliban government in Kabul.
If confirmed, Omar's death would mark a significant blow to an almost 14-year insurgency, which is torn apart by internal divisions and threatened by the rise of the so-called Islamic State group in South Asia.
His death could trigger a power struggle within the movement, observers say.
Insurgent sources claim that Mullah Mansour, the current Taliban deputy, and Omar's son Mohammad Yakoub are both top contenders to replace him.
