A rocket has killed 35 people in a Damascus shopping district in one of the deadliest rebel attacks on the Syrian capital, as bombardment by the government and its allies left dozens of civilians dead in an opposition stronghold.

Tuesday’s attack came as heavy bombardment killed 38 civilians in the shrinking rebel enclave of eastern Ghouta, which is east of the capital.

State media said the opposition fire had hit the area of Jaramana, which residents said was full of shoppers – many buying presents before Mother’s Day.

A taxi driver, who asked not to give his name, said he had been nearby when the rocket hit a street known for its cheap clothes and food shops.

“The place was full of people buying presents for Mother’s Day,” the 41-year-old said.

A nurse in her 30s, who asked not to be named, said the projectile had hit a shopping area “next to a security checkpoint”. “The intensity of the blast was terrifying,” she said.

The Syrian president, Bashar al-Assad, has brought swathes of territory back under his control since the war started in 2011, with help from Russia and allied forces, including Iranian-backed Lebanese Hezbollah militia.

He has recently focused efforts on flushing out the last pockets that escape government control in and around the capital, the largest of them being eastern Ghouta.

A month-long air and ground assault on the area, which was home to around 400,000 residents, has left more than 1,400 dead.

Regime and allied forces have retaken more than 80% of the area and splintered the rump of the enclave into three pockets, each controlled by different rebel groups.

In images broadcast on Sunday, Assad congratulated soldiers in Ghouta, and told them Damascenes would “maybe tell their children in the coming decades how you saved the capital”.

Clashes shook the various zones on Tuesday, with bombardment by the regime and Russia killing at least 29 civilians in the main town of Douma, the Syrian Observatory for Human Rights said.

Another nine civilians were killed in bombardment in other areas of the enclave, according to the Britain-based monitor.

Washington has voiced concern that the chaos in Syria could allow a revival of the Islamic State group, whose “caliphate” collapsed late last year after three years of international military operations.

The jihadists launched a surprise nighttime attack in a southern neighbourhood of Damascus, the Observatory said.

The group’s founder, Rami Abdul Rahman, said the regime was sending reinforcements to retake Qadam, which was attacked from the adjacent Isis-controlled neighbourhood of Al-Hajar al-Aswad.

An AFP correspondent in Douma reported heavy bombardment throughout Monday night that left ambulances struggling to reach the wounded.

Tens of thousands of civilians have fled both the intense bombardment of Ghouta and the deprivations of a siege that lasted five years.

The ramifications are catastrophic, the UN’s high commissioner for human rights, Zeid Ra’ad al-Hussein, told the security council, accusing the Damascus regime of “war crimes” in eastern Ghouta.

But Hussein also warned of another humanitarian catastrophe unfolding hundreds of miles to the north in the Syrian border enclave of Afrin.

The Turkish army and its Syrian proxies – comprising jihadists, former rebels and members of other armed groups – seized Afrin from Kurdish forces on Sunday.

Turkish military police were deployed across the city on Tuesday, as some civilians tried to return to homes and shops looted by Ankara’s Syrian proxies.

The two-month offensive has displaced about 100,000 people, most of them to the town of Tal Rifaat further east, the UN has said.

On Tuesday, a convoy carrying food, blankets and other aid was being delivered to thousands of families seeking refuge in Tal Rifaat, according to the Red Cross.

The capture of Afrin, one of the cantons in the self-proclaimed autonomous administration run by Syria’s Kurds, has been a huge blow to the minority.