President Bashar al-Assad’s troops have tightened their siege of Aleppo, after another 24 hours of intense bombardment that left dozens dead and nearly 2 million without water.

The United Nations security council is due to meet at 11am on Sunday to discuss the escalation of fighting in Aleppo, diplomats said, at the request of the US, Britain and France.

A barrage of bombs has been dropped on the city since Thursday when Assad, along with his Russian backers, abandoned a shaky ceasefire and government forces launched a new assault on the city that was Syria’s largest before the war.

The attack has left US policy on Syria in disarray, with diplomats pursuing a halt in hostilities even as Assad’s forces on the ground ramped up fighting using Moscow’s air power as back-up.

The intensity of the attack and the power of some of the larger bombs are unprecedented even for a city that has endured some of the most brutal fighting of Syria’s long civil war, including years of notoriously imprecise barrel bombs.

On the ground, Syrian troops were pressing their advantage and captured the Handarat camp for Palestinian refugees. Deserted, but strategically important, the camp is perched on elevated ground overlooking the key Castello road into besieged Aleppo.

That route fell to government troops in July, cutting off an estimated 250,000 people, and the latest advances consolidate the siege. “Handarat has fallen,” an official with one of the main Aleppo rebel groups told Reuters.

The scale and nature of the attacks have left Aleppo reeling and dozens dead. Activist groups said more than 50 bodies had been found since midnight on Friday alone. One warned that “people now don’t think they will live to see another day”.

The munitions used appear to include extremely powerful “bunker buster” bombs that can bring down whole buildings. They make death tolls harder to calculate because they destroy some bodies entirely and leave others too deeply buried in rubble for recovery.

The airstrikes have also targeted the headquarters of the city’s famous civilian “white helmets”, who risk their lives to dig survivors from the rubble of bombed buildings. The strikes meant they had fewer men and resources to respond to other attacks, with only two fire engines left, while fuel shortages and roads blocked by rubble are slowing ambulances.

“Our teams are responding, but are not enough to cover this amount of catastrophe,” Ammar al-Selmo, head of the civil defence rescue service in the opposition-held east, told Reuters from Aleppo.

Doctors are struggling to triage the injuries brought into the few remaining hospitals, with medical supplies running out. There are also fears that epidemics could take hold, after water supplies were cut to both sides of the city.

Airstrikes damaged the Bab al-Nayrab pumping station which provides eastern Aleppo with water, and the intensity of attacks meant repair teams could not reach it, the UN said. In retaliation, another nearby station Suleiman al-Halabi – which supplies more than 1.5 million people in government-held western Aleppo – was switched off.

“Depriving children of water puts them at risk of catastrophic outbreaks of waterborne diseases and adds to the suffering, fear and horror that children in Aleppo live through every day,” Hanaa Singer, the representative of the children’s agency, Unicef in Syria, said. “It is critical for children’s survival that all parties in the conflict stop attacks on water infrastructure.”

In the west of the city, some deep wells can provide water, but in east Aleppo most of the well water is contaminated. The charity plans to truck water throughout the city, but warned this is a temporary and inadequate solution.

The US secretary of state, John Kerry, said he had made “a little progress” on halting the violence in talks with the Russian foreign minister, Sergei Lavrov. But the Russians said there was little to suggest any forward movement, so Aleppo’s misery looks set to continue.

Assad is determined to regain control of a city that has become a symbol and a strategic prize for both sides. But, despite the intense bombing, it is unlikely to fall quickly. A large, defiant population remains in rebel-held areas, and they are afraid of the retribution of government forces should they succeed in capturing the city.

“It seems highly improbable that there will be a quick defeat of eastern Aleppo,” one western diplomat told journalists in New York. “The only way to take it is by such monstrous atrocities that it would resonate for generations.”