Air strikes battered neighborhoods around a children's hospital and a blood bank in rebel-held eastern Aleppo on Wednesday in a second day of renewed bombing that has killed at least 32 people, a war monitor, medics and emergency workers said.
The air raids formed part of a wider military escalation by the Syrian government and allies including Russia, which fired coordinated volleys of missiles at rebels on Tuesday and for the first time used its only aircraft carrier.
The Syrian Observatory for Human Rights, a Britain-based war monitor, said the air strikes on eastern Aleppo on Wednesday alone killed at least 21 people, including five children and an emergency worker. They were carried out by either Russian or Syrian warplanes, it said.
The Observatory said districts struck included al-Shaar, al-Sukkari, al-Sakhour and Karam al-Beik.
Moscow has denied reports that its jets hit the city in the renewed wave of bombardment, and said it was sticking to a moratorium on air strikes in Aleppo.
Tuesday's bombing run on eastern Aleppo appeared to mark the end of a pause inside the city declared by Russia on Oct. 18 which Syria's military had also largely observed.
The Observatory and residents said the city's east was hit by rocket fired from jets, barrel bombs dropped from helicopters and artillery from government forces.
"The helicopters won't stop for a single moment," Bebars Mishal, a civil defense worker in rebel-held Aleppo, told Reuters. "Right now, the bombing won't let up."
The Civil Defense is a volunteer rescue service that operates in rebel-controlled areas of Syria, including Aleppo, the country's largest city and commercial hub before the war.
Wednesday's bombing struck next to a children's hospital and blood bank in the Shaar district, and near a school in the Salah al-Din district, residents and the Observatory said.
Two ambulances were also destroyed, said an advocacy officer at the Syrian American Medical Society aid group, citing reports from colleagues in Aleppo.
"We woke up to the bombing and until now, the warplanes and helicopters are running," said Modar Shekho, a nurse in eastern Aleppo. "The Shaar neighborhood was burned down between yesterday and today."
A video posted by Shekho on a social networking site, which he said was taken on Wednesday, showed a building with large holes and burn marks next to a large heap of rubble and twisted metal which he said was all that remained of another structure.
Ibrahim Abu al-Laith, a Civil Defense official, said there were more than 40 air strikes on the Shaar area. "Today the bombardment is very, very fierce," he said.
On Monday and early Tuesday, there were air strikes on hospitals in three rebel-held towns to the west of Aleppo, knocking them all out of service. Damascus and Moscow both deny targeting hospitals.
The World Health Organization said there had been heavy attacks on five hospitals in Aleppo and Idlib provinces since Sunday, severely reducing access to health services for people in northern Syria.
Syrian state television said on Tuesday the Damascus government's air force took part in strikes against what it called terrorist strongholds in Aleppo's Old City.
Russia said it had struck Islamic State and former Nusra Front militant sites elsewhere in Syria, without mentioning Aleppo.
On Tuesday evening, state-owned Ikhabariyah television reported large troop deployments along several main fronts in the Aleppo theatre in preparation for a major ground offensive that it said was imminent and awaiting "zero hour" to begin.
Aleppo has become the pivotal front in Syria's 5-1/2-year war pitting President Bashar al-Assad, supported by Russia, Iran and Shi'ite Muslim militias, against mostly Sunni Muslim rebels including groups backed by Turkey, the United States and Gulf monarchies.
Aleppo has for years been divided between the government-held western sector and rebel-held east, which the Syrian army and its allies besieged during the summer. Its allied forces include Iran's Revolutionary Guards, Lebanon's Hezbollah and Iraqi Shi'ite militias.