MOSCOW - Syrian regime forces were on the verge Tuesday of seizing a major rebel district of Aleppo as Moscow and Washington traded barbs over stalled efforts to end fighting in the battle-worn city.
After retaking control of about two-thirds of east Aleppo in recent days, forces loyal to President Bashar al-Assad were advancing Tuesday on the large residential district of Shaar.
The Syrian Observatory for Human Rights, a monitoring group, said if the district is retaken rebel forces will be reduced to a "war of attrition" with the army.
"It is the most important neighbourhood in the heart of east Aleppo, and is on the brink of falling," Observatory head Rami Abdel Rahman said, adding that regime forces were already in control of about a third of the district.
With the capture of Shaar, the army would hold 70 percent of east Aleppo, four years after rebels first seized it and divided the city.
The regime's rapid gains have left opposition fighters scrambling to defend the shrinking enclave they still control in Aleppo's southeastern districts.
The international community has also struggled over how to respond, despite widespread concern over the fate of tens of thousands of civilians still in rebel-held areas.
Russia, a key Assad ally, had announced talks with the United States in Geneva for Tuesday or Wednesday on organising a full rebel withdrawal from Aleppo leading to a ceasefire.
- 'Attempt to buy time' -
But Russia's top diplomat on Tuesday accused Washington of backtracking on the planned talks to "buy time" for those battling leader Bashar al-Assad.
"It looks like an attempt to buy time for the rebels to have a breather, take a pause and replenish their reserves," Foreign Minister Sergei Lavrov told journalists, saying Moscow had the impression "a serious discussion with our American partners isn't working out."
Lavrov on Monday said that Russian and US experts were to meet in Switzerland on either Tuesday or Wednesday to discuss a proposal put forward by US Secretary of State John Kerry last week on a complete rebel withdrawal from the war-torn eastern sector of Syria's second city.
But on Tuesday he acknowledged that Washington had said it would not take part in Wednesday's talks and had withdrawn the suggestions made by Kerry.
Rebels in east Aleppo have already dismissed any talk of them withdrawing, but Lavrov said they risked being annihilated if they refused to pull out following any deal between Russia and the US.
"In any case, if someone refuses to pull out willingly, they will be destroyed."
Kerry on Tuesday rejected Russian charges Washington was stalling talks on a rebel withdrawal.
"I'm not aware of any specific refusal," Kerry said when asked about Moscow's charges as he attended a NATO foreign ministers meeting in Brussels.
Washington, for its part, accused Moscow of stalling for time after Russia and China blocked a UN Security Council resolution on Monday calling for a seven-day ceasefire.
Russia said the resolution should have been postponed until after the Geneva talks, saying an agreement on organising a withdrawal was close.
The deputy US envoy to the United Nations, Michele Sison, suggested there was no deal, accusing Moscow of using a "made-up alibi" to block the resolution.
"We will not let Russia string along the Security Council," she said.
"We will continue bilateral negotiations (with Russia) to relieve the suffering in Aleppo, but we have not reached a breakthrough because Russia wants to keep its military gains."
The rebels have so far rejected any talk of leaving the city, with Yasser al-Youssef of the leading Nureddin al-Zinki faction describing the proposal as "unacceptable".
"It is for the Russians to leave," he told AFP correspondents.
Rebels have been forced to evacuate several of their strongholds in Syria during the conflict, most recently a string of areas near Damascus.
- Key battleground -
In many cases, they have reached deals with the government after months of siege and fierce fighting, agreeing to lay down their arms in return for safe passage to rebel territory elsewhere.
But the loss of Aleppo would be the biggest blow yet to opposition forces in Syria's civil war, which erupted in 2011 with popular protests calling for Assad's ouster.
More than 300,000 people have since died and millions forced from their homes.
Aleppo, once Syria's celebrated commercial and cultural hub, has been a key battleground of the war and suffered some of its worst violence.
The most recent offensive has left more than 341 people dead in east Aleppo, including 44 children, the Observatory says.
Rebel fire into the government-held west of the city has killed 81 people, including 31 children, in the same period, the monitor says.
Tens of thousands of east Aleppo residents have also fled to different parts of the city, including to government-held areas and other rebel neighbourhoods.
Escalating bombardment of the neighbouring rebel-held province of Idlib has also left dozens dead in recent days.
At least 85 civilians, including 18 children, have been killed in air strikes on Idlib city and surrounding towns since late Saturday, according to the Observatory.
It said both Russian and Syrian government warplanes took part in the bombing raids.