US and Afghan leaders believed the one-eyed, fugitive leader fled to and eventually died in Pakistan, but a new biography says Omar was living just three miles from a major US base in Zabul province, where he died in 2013.

The Afghan government has vehemently denied the claims in "Searching for an Enemy", by Dutch journalist Bette Dam, -- but the Taliban, who are currently in talks with Washington in Doha, told AFP the book's claim that Omar remained in Afghanistan is "true".

Dam -- who spent years reporting in Afghanistan and has also written a book about former Afghan president Hamid Karzai -- described the Taliban chief as a virtual hermit, refusing visits from his family and filling notebooks with jottings in an imaginary language.

She spent more than five years researching the book and interviewed Omar's bodyguard Jabbar Omari, who claimed to have hid and protected him after the Taliban regime was overthrown.

Following the 9/11 attacks in 2001 which led to the fall of the Taliban, the US put a USD 10 million bounty on Omar and he went into hiding in a small compound in the regional capital Qalat, Dam wrote.

The family living at the compound were not told of the identity of their mystery guest, but US forces almost found him twice.

At one point, a US patrol approached as Omar and Omari were in the courtyard. Alarmed, the two men ducked behind a wood pile, but the soldiers passed without entering.

A second time, US troops even searched the house but did not uncover the concealed entrance to his secret room.

Omar decided to move when the US started building Forward Operating Base Lagman in 2004, just a few hundred metres from his hideout.

He later moved to a second building but soon afterwards the Pentagon constructed Forward Operating Base Wolverine -- home to 1,000 US troops, and where American and British special forces were sometimes based -- close by.

He dared not move again, Dam says, rarely going outside and often hiding in tunnels when US planes flew over.

Though he listened to the BBC's evening Pashto-language news broadcasts, even when Omar learned about the death of al-Qaeda supremo Osama Bin Laden he rarely commented on the outside world, the book says.

It says he delegated Taliban leadership after 2001, acting more as a spiritual leader to the group.

The book claims that Omar became ill in 2013 and refused to travel to Pakistan for treatment, later dying in Zabul.

The Afghan government said it "strongly" rejected the "delusional" claim.

"(W)e see it as an effort to create and build an identify for the Taliban and their foreign backers," tweeted Haroon Chakhansuri, a spokesman for the Afghan presidency.

"We have sufficient evidence which shows he lived and died in Pakistan. Period!" Former CIA director and US military commander in Afghanistan David Petraeus also appeared sceptical.

"I would be very surprised if Mullah Omar would have taken the risk that we could come calling some evening," said Petraeus, according to the Wall Street Journal.

"I have piles & piles of evidence which shows he lived & died in Pakistan," tweeted Amrullah Saleh, who was head of Afghan intelligence from 2004-2010.

Afghan officials have repeatedly accused Pakistan of harbouring Taliban insurgents.

For their part, the Taliban -- who at times have been criticised in Afghanistan for their alleged links to Pakistan -- said the claim was accurate.

"This is true," militant spokesman Zabihullah Mujahid told AFP.

"The late Mullah Sahib was in Zabul province all along, and there was an American base nearby, the Americans did carry out a raid there, and he passed away there." Omar's Taliban ruled Afghanistan from 1996 until 2001, and has waged an insurgency since then.

The US and Taliban have remained tight-lipped about the most recent round of talks in Doha, which have been ongoing for two weeks, sparking expectations that they may be inching closer to a deal that could see Washington exit the nearly 18-year conflict.