Russia has intensified its air strikes in an attempt to back up the Syrian government's offensive in Syria's Aleppo, killing scores of people, Al Jazeera has learned.

The reports of deaths come amid another breakdown of peace talks in Geneva and a donor conference in London where world leaders have pledged $10bn to help Syrians.

At least 37 people have been killed, including three children, in suspected Russian air strikes on several neighbourhoods in Aleppo city, a local activist speaking on condition of anonymity told Al Jazeera on on Thursday.

"Syrian and Russian air strikes have targeted al-Bab, Hmeimeh, Soran and several other neighbourhoods in Aleppo province. We can confirm that 37 people have been killed but we are expecting the death toll to rise," he said.

The UK-based Syrian Observatory for Human Rights put the death toll at 21.

Russia launched its military operation in Syria in September 2015, and it says the campaign is against armed groups such as the Islamic State of Iraq and the Levant, which has seized territory in Iraq and Syria, and al-Nusra Front.

Against this backdrop of growing political tensions, Saudi Arabia said on Thursday it was ready to participate in any ground operations in Syria if the US-led coalition decided to start such operations.

The Syrian government launched a major offensive from the north of Aleppo and captured several strategically important towns on Monday.

Syrian forces and their allies broke a three-year rebel siege of the two Shia towns of Nubul and Zahraa in Aleppo province, Syria's official news agency SANA reported on Wednesday, cutting off a main supply route to nearby Turkey.

The breakthrough comes after days of rapid military gains north of the major city of Aleppo, with Russian air strikes playing a key role in the advance.

READ MORE: Inside Aleppo's fight for water and electricity

Nubul and Zahraa, with an estimated 60,000 population, are connected to the border by areas under the control of Kurdish armed groups that provided access.

The towns have been besieged by rebels since 2012, and reaching them had long been a goal of President Bashar al-Assad's government, which has also sought to sever vital rebel supply routes into Aleppo from Turkey.

In a separate development, two women have died owing to malnutrition and the cold in the besieged town of Madaya, activists say.

Abou Ammar, an aid worker in Madaya, west of Damascus, told Al Jazeera that the situation is becoming worse as supplies have began to run out.

"A 16-year old boy died before yesterday because of malnutrition. We told the MSF [Doctors Without Borders] charity that we have at least 64 new cases of people suffering from malnutrition. What was distributed last month is expected to last 30-35 days," Abou Ammar said.

At least 19 people have died of malnutrition since three aid convoys entered the town on January 11.

"We were told to expect further humanitarian aid this week. The previous batch of aid did not include enough medical supplies or medication for diseases such as diabetes.

"Some people are in desperate need of urgent hospitalisation.

"The temperature drops to below zero at night and people are burning anything they can find to stay warm.

"In Syria, we are either bombed or starved to death."

Madaya, which is controlled by opposition fighters, has been under siege by government forces and Hezbollah fighters since July.

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Images of malnourished Madaya residents shocked the world in early January, showing wide-eyed babies without access to milk and elderly men with cavernous rib cages.

On January 31, MSF said that an estimated 320 people in Madaya were suffering from malnutrition, 33 of whom were "in danger of death if they do not receive prompt and effective treatment".

Up to two million Syrians are trapped in sieges by the government or by opposition groups, MSF said last month.

Diplomatic efforts to end the conflict suffered a setback on Wednesday when Staffan de Mistura, the UN Syria special envoy, announced a temporary suspension of talks in Geneva between the opposition and the government.

Following a meeting with the opposition's Higher Negotiations Committee in the Swiss city, de Mistura fixed February 25 as the date for resuming talks.

Earlier on Wednesday, quoting information from the Syrian Network for Human Rights, the opposition accused the Syrian government and Russia of killing at least 300 civilians since the launch of the so-called Geneva III conference on January 29.

The Geneva negotiations are meant to develop a "road map" to end the conflict of almost five years that has resulted in more than 250,000 Syrians being killed.

The conflict has also displaced millions more and sent hundreds of thousands fleeing as refugees to Europe.