SYRIAN government helicopter gunships have struck a suburb of the capital, Damascus, a day after air strikes in the area killed at least 45 people, activists said.

Sunday’s barrage, according to the Britain-based Syrian Observatory for Human Rights, was particularly heavy.

The group said government air strikes and the bombardment of several opposition-held eastern Damascus suburbs killed at least 45 people.

It followed volleys of mortar shells fired into Damascus by rebels in the area that had killed three people, including a child, just hours earlier.

The UN humanitarian chief Stephen O’Brien said he was “deeply saddened” by the rise in violence.

He spoke to reporters in Damascus at the end of a three-day visit during which he travelled to the central Syrian city of Homs and met with officials in the capital.

“This is a tragic reminder of the urgency of finding a political solution and securing a nationwide ceasefire,” he said.

“Such indiscriminate attacks are unacceptable and we must do our utmost to protect innocent civilians.”

There was no immediate word on casualties from the latest attacks, which targeted the south-western suburb of Daraya. In Sunday’s government attacks, another activist group, the Local Coordination Committees claimed as many as 49 people were killed in the Douma, Saqba and Arbeen suburbs.

Fighting on the ground in Syria has intensified even as the international community makes its most serious push yet to restart peace talks between government officials and opposition representatives.

Around 6.5 million Syrians are internally displaced, O’Brien said. About 2 million children are out of school, and 72 per cent of the population has no access to drinking water, he added.

“This situation is unacceptable. A blot on our collective conscience,” he said.

Meanwhile, Russia’s air force is conducting dozens of air strikes in Syria daily to support the Free Syrian Army (FSA) fighting alongside government troops against Daesh militants, the chief of the Russian army’s general staff was quoted as saying yesterday.

The number of FSA fighters now advancing in the provinces of Homs, Hama, Aleppo and Raqqa now exceeds 5,000, Russian news agencies quoted General Valery Gerasimov as telling a meeting with foreign military attaches accredited in Russia.

The Russian military leader said FSA rebels are receiving weapons from Moscow – comments that come just days after a Kremlin spokesman denied the claims.

Gerasimov was quoted by Russian news agencies as saying that Russia is supporting the FSA with air strikes and is also helping “with weapons, ammunition and material”.

Last week, President Vladimir Putin said the rebels, who oppose Moscow’s ally Syrian president Bashar Assad, were receiving weapons from Russia, but Kremlin spokesman Dmitry Peskov later said Putin meant Assad’s army was getting weapons and the rebels were receiving only air support.

FSA’s chief of staff has denied receiving Russian weapons.

Meanwhile on the eve of a visit to Moscow by US Secretary of State John Kerry, Russia has stepped up its criticism of US policy on Syria, saying it had not shown it was ready to cooperate fully in the struggle against Daesh militants.

Russia would continue to urge Washington to rethink its policy of “dividing terrorists into good and bad ones”, Russia’s Foreign Ministry said in a statement.