Jet fighters and helicopters bombing east Aleppo hit a children’s hospital on Wednesday morning, destroying sections of the building as medics and patients sheltered in the basement, reports The Guardian.

An ambulance driver and at least two children were among the dead after a night of fierce attacks on rebel-held sections of Syria’s largest city.

The assault, which continued into the morning, is widely believed to mark the start of a push by President Bashar al-Assad and his backers, including Russia and Iran, to crush the opposition in their last urban stronghold.

“A horrible day for the children’s hospital. Me and my staff and all the patients are sitting in one room in the basement right now, trying to protect our patients,” the centre’s director, Dr Hatem, said in a message posted on Facebook. “We are trying to leave the basement but we can’t because of all the aircraft still in the sky. Pray for us please.”

The children’s hospital, which carries out around 4,000 consultations a month, was one of six medical centres bombed in Syria over the last 48 hours, according to a charity that supports them.

“Like all the surrounding hospitals in eastern Aleppo, it has been hit multiple times this year alone, putting 2016 on track to becoming the worst year of hospital attacks on record,” the Independent Doctors Association said.

The targeting of civilians and medics in Aleppo in particular have fueled international outrage and growing pressure on Damascus to halt the bombing.

But opposition forces are now bracing for an intensified campaign on the city, against the backdrop of a geopolitical landscape dramatically changed by the election of Donald Trump as the next US president.

On Tuesday Assad described Trump as a potential “natural ally” if the president-elect fulfilled a campaign promise to fight terrorism.

Doctors said an ambulance driver had been killed in the airstrikes, and many people were under the rubble after a bombardment that included “barrel bombs” – cylinders packed with explosives dropped often inaccurately from helicopters and usually targeting civilian areas.

“Horror is back to Aleppo,” said Abdulkafi al-Hamdo, a teacher in the city, in a text message. Audio recording from inside the city captured the sounds of intense bombardment and shelling.

Russia has denied involvement in the air raids so far on the city, but said it had launched missile strikes and bombing raids on the provinces of Idlib and Homs on Tuesday from its aircraft carrier the Admiral Kuznetsov, which is stationed off the Syrian coast. The aircraft carrier’s arrival in a highly publicized trip was heralded as signifying the start of the campaign to reclaim Aleppo.

Whole districts of a city that was once Syria’s most vibrant have been virtually abandoned over years of intense street fighting, and many parts of the east have been bombed to rubble. Opposition areas are being starved by a slowly tightening siege.

A semblance of normal life continues in west Aleppo and regaining full control of the city would be a huge boost for forces loyal to Assad, for its symbolic value and because it is the only key urban area still controlled by the opposition.

Assad’s forces, backed by Iranian and other Shia militias and Russian air power, have used a policy of bombing the opposition to the negotiating table while starving the communities that support them into surrender in several Syrian cities. They appear to be deploying the same tactics in Aleppo.

The situation in Aleppo has long been seen as a bellwether for the broader civil war in Syria, and the current onslaught is within the context of surging momentum for the Assad regime after Moscow’s intervention in the war last year.

The opposition also fears that the Trump administration will abandon America’s covert but limited support for the rebellion, allowing the Kremlin a free hand to crush it. Trump said during the election campaign that he intended to focus on destroying Islamic State.

In his first reaction to Trump’s election victory, Assad struck a cautious note, saying the president-elect would be a natural ally if he sought to combat terrorists, an epithet that the Syrian president uses to describe all of the opposition.

“We cannot tell anything about what he’s going to do, but if … he is going to fight the terrorists, of course we are going to be ally, natural ally, in that regard with the Russian, with the Iranian, with many other countries,” he told Portugal’s RTP state television, speaking in English.

“I would say this is promising, but can he deliver?” Assad added.