AMMAN/DAMASCUS/BEIRUT: The Syrian army, supported by Russian jets and Iranian-backed militias, escalated bombing Sunday of areas of the Syrian city of Deir al-Zor still held by Daesh (ISIS). The intensified effort came as Damascus said it still considers Raqqa an occupied city, less than two weeks after a U.S.-backed alliance drove Daesh out of its de facto Syrian capital.

Former residents and the Britain-based Syrian Observatory for Human Rights said there were heavy airstrikes on Deir al-Zor as troops pushed toward the Hay al-Umal area, which overlooks some of the remaining militant-held neighborhoods where an estimated 1,500 civilians are trapped.

The Syrian army has gradually tightened the noose around the militants after it opened a land route into the city in September with the help of Russian airstrikes and Iran-backed militias, breaking a siege that had lasted nearly three years.

“The situation is catastrophic, there are families under the rubble and others who fled have no shelter,” said Sheikh Awad al-Hajr, a tribal leader, referring to the plight of those remaining inside the city and in cities, towns and farms in the fertile strip along the Euphrates bordering Iraq.

Fighting and relentless airstrikes in Deir al-Zor province, the last stronghold of Daesh, have prompted tens of thousands of civilians to flee, former residents and aid workers say.

Relatives of some civilians and Syrian opposition figures accuse the Russian army of bombing boats and dinghies carrying families fleeing the western banks of the Euphrates.

Moscow denies it targets civilians in its military operations in Syria and says it hits only militant hideouts and facilities.

Also Sunday, the Syrian Foreign Ministry said in a statement it still considers Raqqa an occupied city.

“Raqqa is still an occupied city and cannot be considered liberated until the entry of the Syrian army, which is fighting IS [Daesh] along with its allies,” the official SANA news agency reported the statement as saying.

“The allegations of the United States and its so-called alliance concerning the liberation of the city of Raqqa from the terrorist group IS are pure lies,” it added.

It said the goal of the U.S. was to “divert the eyes of the international community from the crimes committed by this alliance in the province of Raqqa.”

That was a reference to the U.S.-led coalition’s deadly bombing campaign in the region.

In other developments, while the Syrian army appeared to make more gains inside Deir al-Zor city, Daesh made a surprise offensive during the weekend that pushed back pro-government and Iranian-backed militias from Albukamal, the last border post on the Syrian-Iraqi border still in militant hands.

The Observatory and former residents said the militants recaptured the strategic towns of Al-Qwaira and Makhan Saturday in several deadly ambushes that inflicted heavy casualties on pro-government and Iranian Shiite militias.

The latest militant assault pushed back the army to the city of Mayadin, further north along the Euphrates, which the militants lost earlier this month.“The Islamic State [Daesh] was able to push back the regime and its Iranian-backed militias to the heart of the city of Mayadin,” said Amer Huweidi, an activist from the city in touch with locals and residents.

Mayadin is a strategic city that has been a base for the militants after they were driven out of Raqqa.

The U.S.-led coalition against Daesh is waging a separate campaign against the group in Deir al-Zor, focused on areas to the east of the Euphrates River, which bisects the province.

The coalition secured the Omar oil field, Syria’s largest oil field, this month.

Opposition activists reported at least 11 civilians were killed and a school day violently interrupted amid intensive Syrian government shelling of a rebel-held enclave north of Damascus Sunday, sending panicked kindergarten children scurrying for shelter.

The Observatory and the Eastern Ghouta Media Center said those killed in the Saqba and Hammourieh districts include two women, one child and a media activist. The Eastern Ghouta Media Center said the media activist worked for the local al-Jisr TV.

In a video posted by the Eastern Ghouta Media Center, kindergarten children were seen running in the streets of Kfar Batna, another village in the area that was shelled. Panicked children were scattered in the small rural streets of the village, some in tears while others called out for their parents.

Rescuers struggled to escort the children out of the area covered in a cloud of dust following the explosions.

The first-responders group in the Damascus suburbs, the Syrian Civil Defense, also known as the White Helmets, reported that two shells fell in a school in the center of the village, injuring several.