WASHINGTON: After 10 months of secret dialogue with Afghanistan's Taliban insurgents, senior US officials said the talks have reached a critical juncture and they will soon know whether a breakthrough is possible, leading to peace talks whose ultimate goal is to end the Afghan war.

As part of the accelerating, high-stakes diplomacy, the United States is considering the transfer of an unspecified number of Taliban prisoners from the Guantanamo Bay military prison into Afghan government custody.

It has asked representatives of the Taliban to match that confidence-building measure with some of their own. Those could include a denunciation of international terrorism and a public willingness to enter formal political talks with the government headed by Afghan President Hamid Karzai.

The officials acknowledged that the Afghanistan diplomacy, which has reached a delicate stage in recent weeks, remains a long shot. Among the complications: U.S. troops are drawing down and will be mostly gone by the end of 2014, potentially reducing the incentive for the Taliban to negotiate.

Still, the senior officials, all of whom insisted on anonymity to share new details of the mostly secret effort, suggested it has been a much larger piece of President Barack Obama's Afghanistan policy than is publicly known.

U.S. officials have held about half a dozen meetings with their insurgent contacts, mostly in Germany and Doha with representatives of Mullah Omar, leader of the Taliban's Quetta Shura, the officials said.

The stakes in the diplomatic effort could not be higher. Failure would likely condemn Afghanistan to continued conflict, perhaps even civil war, after NATO troops finish turning security over to Karzai's weak government by the end of 2014.

U.S. officials have met with Tayeb Agha, who was a secretary to Mullah Omar, and they have held one meeting arranged by Pakistan with Ibrahim Haqqani, a brother of the Haqqani network's founder. They have not shut the door to further meetings with the Haqqani group, which is blamed for a brazen attack this fall on the U.S. embassy in Kabul and which senior U.S. officials link closely to Pakistan's intelligence agency.

Success would mean a political end to the war and the possibility that parts of the Taliban - some hardliners seem likely to reject the talks - could be reconciled.

On Sunday, a senior member of Afghanistan's High Peace Council said the Taliban had indicated it was willing to open an office in an Islamic country.

But underscoring the fragile nature of the multi-sided diplomacy, Karzai on Wednesday announced he was recalling Afghanistan's ambassador to Qatar, after reports that nation was readying the opening of the Taliban office. Afghan officials complained they were left out of the loop.

U.S. officials say they have kept Karzai informed of the process and have met with him before and after each encounter, but they declined to confirm whether representatives of his government are present at those meetings.