NEW YORK, Sept. 30 (UPI) -- As the United States and opposition forces continue to tangle with Russia and Bashar Assad's regime in Syria, President Barack Obama's chief diplomat is becoming increasingly frustrated at the lack of progress, a new audio recording indicates.
Friday, The New York Times published excerpts of a tape that was recorded last week during the United Nations General Assembly -- in which Secretary of State John F. Kerry is heard backing the U.S.-led effort to end Syria's civil war, but also voicing concerns that it's getting more difficult to achieve peace.
During a 40-minute discussion with Syrian civilians in New York, Kerry expressed sympathy and disappointment that the U.S. government hasn't been more willing to consider military options in the war-torn nation.
For one thing, he reportedly said, recent U.S. efforts at peace-driven diplomacy should have been backed by a greater threat of force.
"I think you're looking at three, four people in the administration who have all argued for use of force, and I lost the argument," he said.
He also said the U.S.-led coalition forces don't have legal justification to attack the Assad regime, while Russia operates with the approval of Damascus' government.
"The problem is the Russians don't care about international law, and we do," Kerry told the Syrian nationals.
"You have nobody more frustrated than we are."
A cease-fire organized by Kerry and Russia's foreign ministry earlier this month didn't last a week before it collapsed, and led to the resumption of Russian and Syrian airstrikes against various targets -- including highly-contested Aleppo, which may now be verging on collapse.
The World Health Organization said this week that nearly 350 people had been killed by the airstrikes, including about 100 children. A convoy carrying relief aid to Aleppo was also destroyed by airstrikes earlier this month, further upsetting negotiators in the peace process.
Two senior U.S. officials told NBC News Friday that strategists are worried that Aleppo might not stand much longer -- particularly because thousands of ground troops are gathering for an offensive to push opposition forces out of the city.
At this point, the officials said, they hope rebels and residents in Aleppo can hold out for a few more weeks. The U.S. Department of State said Aleppo's collapse might come sooner rather than later.
"It's hard to say when and if a city or population center could fall. But, you know, given the uptick in violence, given the intensity of it, it's hard, it's, it could be soon, " State Department spokesperson Mark Toner said Friday.