Russian and Syrian air raids on the rebel-held eastern half of the city of Aleppo have forced the closure of the largest hospital in the area and killed two people, a medical charity says.
The Syrian American Medical Society, which supports the hospital, said it had been struck by barrel bombs.
There are also reports of Russian-backed Syrian government forces hitting Aleppo's historic Old City.
Clashes between government troops and rebels are occurring in several areas.
Russian and Syrian air forces resumed attacks on the rebel-held east of the city after a partial truce lapsed on 19 September. Government forces have also launched a ground offensive against the rebels.
The mounting civilian death toll has sparked international protests. The US says Russia is driving moderate rebels into the arms of jihadists.
Once Syria's commercial and industrial hub, Aleppo has been divided roughly in two since 2012.
The UN says at least 400 civilians, including many children, have been killed in the city this week as a result of Russian and Syrian government attacks.
On Saturday, air raids hit Aleppo's main trauma M10 hospital for the third time in a matter of days, medical workers say.
"The hospital is now out of service completely," radiologist Mohammad Abu Rajab was quoted by Reuters as saying.
"There's destruction to walls, infrastructure, equipment and generators. There are no more guards or staff left. It's complete darkness."
Hospital manager Dr Abu Rajan told local media that about 10 people at the hospital had been injured after it was hit by barrel bombs - improvised devices dropped from helicopters - cluster munitions, and a chlorine bomb.
Two patients were killed, while others have now been transferred to alternative facilities, the Syrian American Medical Society said.
A spokesman for US President Barack Obama condemned the bombing, which he said showed "total disregard" for medical professionals and patients.
"Reports of yet another hospital being destroyed further demonstrates the total disregard for the lives of medical professionals and their patients who need critical care because of the Assad regime and Russia's relentless campaign against the Syrian people."
French Foreign Minister Jean-Marc Ayrault also condemned the bombing, saying the shelling of healthcare structures and personnel constituted war crimes - and the perpetrators would have to be held to account.
The Syrian army says it is gaining ground but the rebels deny this.
"They are shelling the Old City heavily after another failed attempt to gain ground," Abu Hamam, from the Failaq al-Sham group, was quoted as saying by Reuters news agency.
"They have lost several fighters and we are steadfast."
The Syrian Observatory for Human Rights, a UK-based monitoring group, also reported government barrel bomb and jet attacks on the Ghouta area outside Damascus on Saturday.
In another development, it said government forces were battling fighters from the Islamic State group in Homs region.
War of words
Washington and Moscow have continued to spar over Syria, with the US dismissing Russian accusations that it was protecting a jihadist group in its bid to oust Syrian President Bashar al-Assad.
Russian Foreign Minister Sergei Lavrov said the US had broken its promise to separate the powerful Jabhat Fateh al-Sham (formerly known as al-Nusra Front) and other extremist groups from more moderate rebels.
State department spokesman Mark Toner said the Russian allegations were "absurd".
He told reporters the US had not targeted al-Nusra for months because they had become "intermingled" with other groups and civilians.
At least 250,000 people have been killed in the conflict since it began in March 2011 with the Observatory estimating the true number to be about 430,000.
More than 4.8 million people have fled abroad, and an estimated 6.5 million others have been displaced within the country, the UN says.