GAZIANTEP, Turkey >> The United States and its allies have spent many millions of dollars backing Syrian opposition fighters they deem relatively moderate and secular, and civilian groups whose work on small businesses and local councils they billed as the cornerstone of Syria’s future.

But the very Syrians who benefited — and risked their lives in the process — now say that investment risks going down the drain, and they see little urgency from Washington, diplomatic or military, to save it.

“What are you going to do, other than statements?” Zakaria Malahifji, the political chief of one of the largest rebel groups given weapons and salaries by the CIA and its counterparts in several European and Arab states, demanded in a recent message to contacts at the French Embassy.

In nearly five years of war and insurrection, many Syrians have been repeatedly disillusioned by what they saw as a mismatch between tough American rhetoric against the Syrian government and comparatively modest efforts to aid some of its opponents. President Barack Obama said President Bashar Assad must go, and drew a red line over the use of chemical weapons, but backed off on both, diminishing anti-government Syrians’ trust.

But the confusion and despair has reached a new level during the last week, as forces backing Assad have pushed further north into Aleppo province, sending tens of thousands of new refugees to the Turkish border. With insurgent groups losing troops and territory, their villages shattered by Russian warplanes, civilians and fighters have in recent days used phrases like “no hope,” “it’s finished” and “it’s over.”

“Bye-bye, revolution,” Abu al-Haytham, a spokesman for Thuwwar al-Sham, another rebel group supported through the CIA program, said in a text message Friday from Tal Rifaat, a town in northern Aleppo that is increasingly threatened by the government advance.

U.S.-backed insurgents have long been used to the American stance in recent years, that the United States did not want them to actually win the war — lest a sudden toppling of Assad lead to Islamist rule — but wanted to prevent them from losing for long enough to pressure the government to negotiate for a political solution.

Now they fear that the United States and its allies may actually let them lose. Many of the rebel leaders who have received Western support were headed Tuesday night to meet with U.S. officials and others in Istanbul and Ankara, but they were not hopeful for game-changing developments.

The Obama administration has said for months that there is no military solution to the conflict in Syria, and that its plan for confronting the chaos inside the country was to try to forge a political transition through United Nations-led talks that would ultimately lead to Assad’s departure. But as those negotiations faltered last week amid heavy bombings by the Syrian government backed by Russia, it was clear that the strategy was doing nothing to change the dynamic on the ground.

Secretary of State John Kerry was left berating Russia publicly for failing to live up to its commitments to pursue a cease-fire and allow humanitarian access inside Syria, while making a frantic round of phone calls to Sergey V. Lavrov, the Russian foreign minister, to try to salvage the political talks.

Kerry has been subject to increasing criticism, after an incident last week in which Syrian civil-society workers buttonholed him at a London cocktail party thrown by Prince Charles after an international donors’ conference on Syria. According to one of the Syrians who was there, who spoke on the condition of anonymity to protect her organization, the Syrians asked the secretary to put more pressure on Russia and the Syrian government to stop attacks and sieges on civilians.

The activist said Kerry seemed to blame the opposition for refusing to participate in U.N.-led talks in Geneva, and when the Syrians mentioned that 230 barrel bombs had fallen on Aleppo that day, he corrected them.

Then, she said, he added: “It’s going to get much worse. This will continue for three months, and by then the opposition will be decimated.” Pressed further, Kerry said, “What do you want me to do, go to war with Russia?”

As this story rocketed around social media, the State Department spokesman, John Kirby, declared Monday that Kerry was “making no predictions about three months this or three months that.” On Tuesday, Kirby told reporters that “there’s been no badgering of the opposition,” and that Kerry simply objected to the rebel groups’ placing “preconditions” on the negotiations.

“If you put preconditions on it, you make it too easy, certainly for the regime and its supporters, to use that as an excuse not to talk and not to sit down and not to begin any dialogue,” Kirby said.

Opposition representatives say they are not imposing preconditions but asking for the implementation of existing U.N. Security Council resolutions to end starvation sieges and indiscriminate bombings, tactics forbidden under international law, and that access to aid should not be subject to negotiations.

Here in Gaziantep, the rebel representative, Malahifji — whose group’s Koranic name translates to Go Straight As You Were Commanded — was one of several Syrians worried that the government and its allies could fight all the way to the Turkish border within weeks. Asked about the chance of retaking areas lost during the past week in Aleppo province, Malahifji, who is originally from Aleppo’s old city, gave a deep sigh.

“We need real diplomatic pressure or air support, and we don’t have either,” he said, adding that rebels could recover ground only if the United States allows its allies to give them anti-aircraft missiles. That is unlikely because of fears they could fall into extremist hands.

Still, he warned that even if the government routs rebels from northern Aleppo province, it would not end the conflict. “They can capture it, but they can’t rule it,” Malahifji said. “They will not last long, but now we are looking at a humanitarian catastrophe.”

Along parts of Syria’s frontier with Turkey, aid agencies reported a drastic increase in the number of people fleeing the Aleppo area, where there have been more than 200 airstrikes a day.

Doctors Without Borders, a medical charity, said roughly 23,000 Syrians were massed near the border town of Azaz, adding to the pressures created by tens of thousands of displaced Syrians already encamped in the region. “There is an urgent need for shelter, water access, sanitation, and showers, and specific nonfood items such as blankets and insulating mattresses for displaced families,” the charity said in a statement.

The U.N. refugee agency implored Turkey — which already houses more than 2.5 million Syrian refugees, the most of any country — to allow “a broader access to Turkish territory for all those in need of international protection.”

The agency also asked for other nations to “swiftly and meaningfully increase support to Turkey.”

Huddled in restaurants and offices around Gaziantep, Syrian and international development workers were more bereft than ever.

Dahham, who uses a nickname to protect family back in Syria and to avoid jeopardizing aid by criticizing the West, said programs he had worked on, to build up village economies, were now in jeopardy.

Aside from the blow to the villages, he said, “It’s a waste of money” for the backers.

A group of international aid workers sat in a cafe discussing what they called “the million-dollar question”: how to respond to Syrian partners who were calling in despair and asking if their work had been in vain.

Their projects with refugees in Turkey and with communities inside Syria, they said, were predicated on the idea that one day, the refugees would return and the towns would govern themselves.

Now, they said, those Syrians would be more likely to think of joining the flow of refugees.

“What happened in Aleppo really takes away a lot of the hopes for that transitional future,” one worker said. “How do you tell someone, ‘You need to stay engaged,’ when their home village just took hundreds of bombs in a day?”

© 2016 The New York Times Company