WASHINGTON: Reclusive Taliban leader Mullah Mohammad Omar wrote to President Barack Obama last year indicating an interest in talks key to ending the war in Afghanistan, current and former US officials told The Associated Press.

The letter purportedly from Omar was unsigned.

It was passed through a Taliban intermediary in July and was intended for the White House.

The officials spoke on condition of anonymity because the letter and its contents are part of sensitive diplomacy with a fighting force that still targets US troops.

The previously undisclosed communication was considered authentic by people who saw it, but skeptical administration officials said they cannot determine it actually came from Omar.

The Obama administration did not directly respond to the letter, two officials said, although it has broadened contacts with Omar's emissaries since then.

Sources who described the letter did not disclose its precise contents, but one current and one former official said it addressed Taliban willingness to build trust with the United States.

One official said Omar complained that the United States had not done enough to establish good faith for negotiations, such as arranging the release of Taliban prisoners held in the US military prison at Guantanamo Bay, Cuba.

An administration official would say only that the message represented views consistent with what Taliban emissaries had been telling US officials during the clandestine meetings.

Those preliminary sessions opened the way for more formal talks that the US officials now publicly welcome.

A direct message from Omar could be a strong signal that the Taliban movement is interested in negotiation at the highest levels.

The Obama administration is trying to foster talks among the Taliban and the US-backed government of Afghan President Hamid Karzai, but remains wary of Taliban motives.

Omar is the spiritual leader of the Taliban movement, and directs the organisation's guerrilla military campaign.

He was the de facto head of state in Taliban-controlled Afghanistan prior to the US invasion that toppled the Taliban government in 2001.

He has not been seen in public in years, and his exact whereabouts are unknown.

He is wanted by the US government for harbouring Osama bin Laden and helping the al Qaeda terror network.

Republican critics, including presidential candidate Mitt Romney, have criticised the administration for opening talks with an enemy force, saying negotiation only allows the Taliban to run out the clock until most US forces leave Afghanistan in 2014.

Preliminary, clandestine meetings between US and Taliban representatives began last year, after the Obama administration shifted course and decided to explore peace talks while fighting was still fierce.

The message arrived when those early contacts had gone all but dormant, however, because of leaks to the press that sent the chief Taliban emissary briefly underground.

The Obama administration is now considering release of five top Taliban leaders from Guantanamo as a starting point for negotiations.

The five would be sent to custody in the Gulf nation of Qatar, where the Taliban plan to establish a negotiating office. Republicans in Congress oppose the release of the prisoners.