With the Syrian city of Aleppo facing a new regime onslaught and Washington's diplomacy under criticism for failing to halt the carnage, the United States announced a new aid package Tuesday.
The State Department said it would release a further $364 million to UN aid agencies and NGOs working to help vulnerable Syrian civilians inside and outside the war-torn country.
The latest slice of funding brings the total amount that the United States — the effort's biggest single donor — has spent since the war started more than five years ago to $5.9 billion.
But the assistant secretary of state for population, refugees and migration Anne Richard confirmed it would come from funds already allocated by Congress and does not represent new US spending.
"And this is probably... our last announcement of the fiscal year," she told reporters at a briefing to announce the measure three days before the end of the 2016 government spending period.
She also said the United States had admitted some 85,000 refugees over the past fiscal year, which ends on September 30. That figure included about 12,500 Syrian refugees, exceeding the administration's goal of 10,000, she said.
US State Department spokesman Mark Toner said the push for additional humanitarian aid funds came in part because of deteriorating conditions in Aleppo after the collapse of a ceasefire sponsored by the United States and Russia.
"Until the past few weeks we felt like we were on a firm path towards a possible diplomatic resolution to this. We still believe that's possible," Toner told a briefing.
"That doesn't mean we're not mindful ... of the tremendous humanitarian suffering that's going on right now in Aleppo. And that's why we're working so hard to ramp up our assistance," he added.
While saying the United States continued to seek a diplomatic resolution of the problem, he left the door open to other action.
He also noted the United States has warned that failure to achieve a ceasefire could lead to an escalation of the conflict.
The civil war in Syria erupted in early 2011, when Bashar al-Assad unleashed a brutal clampdown on anti-regime protests, and has since killed more than 300,000 people.
Millions have fled their homes, with many living in makeshift camps inside Syria or its neighbours Turkey, Jordan and Lebanon, reliant on UN agencies funded by major UN members.
The United States and Russia, which back the opposition and regime respectively, announced a ceasefire on September 9. It lasted barely a week.
As the deal collapsed, Assad's regime launched a major offensive against the opposition-held east of Syria's commercial hub, Aleppo, backed by waves of Russian bombers.
The diplomatic initiative's failure has exposed President Barack Obama's White House to criticism that, having no back-up plan, it has effectively ceded the initiative to Russia.
White House spokesman Josh Earnest insisted on Tuesday that Obama "and his team are always looking carefully at the situation to determine if there is something different that we can do."
But the violence in Aleppo is such that air-dropping aid would be too risky, he said, while arming the opposition forces would "only further militarise a situation that doesn't have a military solution."
Opposition forces control almost half of Aleppo. The UN says more than 250,000 people live in the opposition-held areas of Aleppo, while more than 1 million are in the regime-controlled part that is usually subjected to shelling.
The World Health Organization called for the "immediate establishment of humanitarian routes to evacuate sick and wounded" from the besieged eastern part of the city.
Having been under the control of opposition forces throughout most of Syria’s five-and-a-half-year civil war, eastern Aleppo has endured endless airstrikes and barrel bombings, leaving much of its infrastructure in ruins.
Only seven hospitals, some only partially operational, are still standing the city’s opposition-held districts, where only around 30 doctors remain.
Assad's regime controls the capital city of Damascus, except for two small neighbourhoods. It also controls all of Homs and Hama, the third- and fourth-largest cities.
Aleppo is the last of the major cities still being contested, and it could take regime forces between six months and a year to capture it, unless they aim to "annihilate" the politically significant city, a Western diplomat said.
The envoy, who is familiar with the cease-fire talks that have faltered, spoke on condition of anonymity because of his government's regulations.
Once all of "useful Syria" is in the regime's hands, international diplomacy would have to determine the fate of the opposition-controlled northwest and those areas dominated by YPG and DAESH.
Regime leader Bashar Assad "doesn't want a negotiation," the diplomat said, adding that "the Russians wouldn't or couldn't stop him" from attacking Aleppo.
Regime launches Aleppo ground attack
Syrian regime forces and their allies attacked the opposition-held sector of Aleppo on several fronts on Tuesday, the biggest ground assault yet in a massive new campaign that has destroyed a US-backed ceasefire.
Regime forces and allied militia from Iran, Iraq and Lebanon, attempt to attack Aleppo's Old City near its historic citadel, as well as around several of the city's major access points.
The United States says the assault on Aleppo is proof that regime leader Bashar al-Assad and his Russian and regional allies have abandoned an international peace process to pursue victory on the battlefield after nearly six years of civil war.
Quelling the uprising in the city would give Assad his biggest victory yet of the war and deliver a powerful blow to his enemies.
It is far from clear whether an all-out attempt to storm the opposition-held area is planned soon: that would require a massive assault by the regime forces, backed by Lebanese and Iraqi militias, Iran's Revolutionary Guards and Russian air power.
The regime's strategy in other locations such as Damascus and Homs has been to use years of siege and bombardment to force eventual surrender, rather than attempting to storm well-defended territory.
In Russia, Deputy Foreign Minister Mikhail Bogdanov told Syrian regime's ambassador that Moscow has "a firm intention to continue providing assistance to the Syrian regime in fighting terrorism and to help achieve the soonest possible political settlement of the Syrian crisis."
However, Assad's other allies now openly say they have abandoned the peace process and are betting instead on military victory.
"There are no prospects for political solutions ... the final word is for the battlefield," the leader of Lebanon's Hezbollah Shi'ite movement, Sayyed Hassan Nasrallah, was quoted in a Lebanese newspaper as saying on Tuesday.
The head of Iran's National Security Council, Ali Shamkhani, was quoted on Tuesday as saying Aleppo's fate would be determined only "through a forceful confrontation".
Aleppo residents said the ferocious air attacks of previous nights had abated somewhat.
The regime-run television reported that the Assad's forces had retaken al-Farafra district in Aleppo's Old City and engineering units were clearing mines in the area.
A senior opposition source said the regime had taken some positions near that area, but had been forced to withdraw.
Neither assertion could be independently confirmed.
The regime's forces had also been repelled after heavy fighting in assaults on four other fronts, he said, describing it as the biggest wave of ground attacks since the offensive was announced last week.