So far, however, those signs are hazy at best, according to officials and diplomats.

American officials have participated in three meetings this year with an English-speaking Afghan who was once a personal assistant to the renegade Taliban leader Mullah Muhammad Omar. Those meetings, in Germany and Qatar, appear to have accomplished little more than confirming the man’s identity, and perhaps not even that, according to officials familiar with the talks, all of whom requested anonymity to discuss the secret talks.

Adding another layer of complexity to the already murky effort, the English-speaking Afghan, Tayeb Agha, who was an aide to Mullah Omar during the Taliban’s rise to power, was arrested by Pakistani authorities last year and then released, leading American officials to assume that he is negotiating on behalf of the Taliban with the blessings of the Pakistani authorities.

“We’re at that stage where it’s very confusing,” one senior administration official said, adding that the meetings could not even be called “talks” at this stage, let alone “peace talks.”

The wariness in part reflects the fact that the administration has been badly embarrassed by previous diplomatic efforts. An Afghan was given substantial sums of cash last year and was flown on a NATO aircraft in the belief that he was a Taliban envoy, but he turned out to be an impostor.

Even so, the renewed diplomatic push signals a significant shift in Mr. Obama’s strategy since he came to office in 2009 and increased American forces in Afghanistan to nearly 100,000 troops, from 34,000, in an effort to crush a resurgent Taliban insurgency.