Government forces further push into rebel-held areas as Russia and China veto ceasefire plan for besieged Aleppo.

Syrian government forces gained more ground in the battle for Aleppo on Monday, as Russia and China vetoed a UN Security Council resolution that sought a seven-day truce in the battered city.

Three weeks into their offensive, the army and allied militias seized the Qadi Askar neighbourhood overnight and were in control of about two-thirds of the former rebel territory in east Aleppo.

“The Syrian government and its allies are now about 800 metres from the citadel … They’re now in control of about 60 percent of what used to be the rebel-controlled east,” Al Jazeera’s Stefanie Dekker said, reporting from Gaziantep along the Turkey-Syria border.

The UK-based Syrian Observatory for Human Rights said the latest advances had left the large al-Shaar neighbourhood effectively encircled by government forces.

Observatory director Rami Abdel Rahman said the army was attacking both from inside east Aleppo as well as from the government-held western districts.

“The regime is draining the rebel fighters of ammunition by opening many fronts at the same time,” he said.

The rebels defending al-Shaar may be forced to abandon it or risk being cut off from the other areas.

The Syrian army could not immediately be reached for comment.

“The regime advanced [into al-Shaar] and there were clashes all night. The clashes are still going on,” Zakaria Malahifji, a Turkey-based official with the Aleppo rebel group Fastaqim, told Reuters news agency.

A fighter with the Nour al-Din al-Zinki group in Aleppo said government forces had made advances on several fronts, putting al-Shaar under pressure, but it had not yet been besieged.

A rebel official in a third rebel group, the Jabha Shamiya, said al-Shaar had effectively fallen since government forces seized nearby areas that control access to it.

“Karm al-Jabal and al-Shaar are considered fallen,” the official with the Jabha Shamiya group told Reuters, speaking from Turkey.

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President Bashar al-Assad’s forces have made steady gains since launching the assault to retake all of rebel-held east Aleppo nearly three weeks ago. Its loss would mark the biggest defeat for rebel forces in Syria’s five-year civil war.

Tens of thousands of east Aleppo residents have fled to other parts of the city to escape the fighting, which has raised widespread international concern.

Russia vetoed Monday’s resolution arguing that ceasefire would allow rebels to regroup, and that time was needed for talks between Washington and Moscow.

It was the sixth time Russia has vetoed a Security Council resolution on Syria since 2011 and the fifth time China has blocked action. The remaining 11 council members voted in favour.

Earlier, Russian Foreign Minister Sergey Lavrov had slammed the proposed temporary truce as a “provocative step”.

“Taking into account all aspects and the current development of the situation, the draft resolution coming against the backdrop of the Russian-American initiative is for the most part a provocative step that undermines Russian-American efforts,” Lavrov told a press conference.

He also said Moscow was confident that it would reach a deal with Washington in talks this week on the withdrawal of all rebels from eastern part of the city, adding that rebel fighters who refused to leave the city would be treated as “terrorists”.

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“We know that Russia and the US consider [Jabhat] Fateh al-Sham a ‘terrorist’ organisation, which was formerly known as al-Nusra Front and linked to al-Qaeda. Now they’re saying, ‘if you don’t leave, all of you are going to be treated as terrorists,'” said Al Jazeera’s Dekker.

Russia has said all rebel groups must leave the area before it allows any access to humanitarian aid.

The Observatory says at least 319 people – including 44 children – have been killed in east Aleppo since the offensive began some three weeks ago.

Rebel fire on the government-held west of the city has killed 69 people, including 28 children, in the same period, the monitor says.

The White Helmets, a volunteer rescue group that operates in rebel-held areas, said that at least 24 people were killed and 85 injured in air strikes and shelling on Monday.

The latest government offensive has added to the misery in east Aleppo, which has been targeted by relentless government fire since it fell to rebels in 2012.

The city’s east was surrounded by government forces in mid-July, and no aid has entered the area since.

International aid provisions have been exhausted and other food supplies are dwindling, meaning many residents are surviving on a single meal a day.

Violence has continued elsewhere in the country alongside the Aleppo fighting, with at least 72 people killed in air strikes and barrel bomb attacks across the northwestern province of Idlib on Sunday, the Observatory said.

Most of those killed died in air strikes on the towns of Maaret al-Numan and Kafr Nabal, the monitor said, adding that those strikes appeared to have been carried out by Russia.