Russia said it had begun a "major operation" which saw the first bombardments carried out by warplanes taking off from its aircraft carrier.
Russia's resumption of air strikes in Syria on Tuesday has triggered a stern reaction from the United States, with Washington calling the targeting of hospitals and civilians "a violation of international law."
The renewed bombing by Russian warplanes on opposition strongholds in the besieged eastern neighbourhoods of Aleppo coincided with multiparty talks in Geneva.
The US, Russia and other countries participating in the talks hope to achieve a cease-fire between Bashar al Assad's regime forces and opposition groups, and a road map toward a political settlement to end the nearly six-year-old conflict.
"We strongly condemn the resumption of air strikes in Syria by the Russians as well as the Syrian regime," US State Department spokeswoman Elizabeth Trudeau told reporters at a briefing.
"The most recent reported attacks were on five hospitals and one mobile clinic in Syria. We believe it's a violation of international law," she said.
At least five people were reportedly killed in the new waves of air strikes by Russian planes and barrel bombings by the Assad regime, the Britain-based Syrian Observatory for Human Rights said.
The strikes hit the Sakhur, Fardos and Masakan Hanano neighbourhoods while ambulances sped through the streets to evacuate the wounded, AFP reported.
According to the the Observatory, the incident was the first of its kind since Russia suspended its air strikes on Aleppo on October 18.
But Trudeau said Russia had allowed no food or other aid into east Aleppo during its suspension of bombing.
"It let eastern Aleppo residents starve while seeking praise from the international community for halting indiscriminate strikes for three weeks," Trudeau said.
"Russia had an opportunity here to facilitate aid and food and medicine to these people who are under siege. It failed to do so," she added.
More than 250,000 people are stuck in the besieged eastern Aleppo neighbourhoods as regime forces continue to pile up the pressure on opposition forces in control of the area. The regime launched a new assault on September 22 in a bid to seize of all of Aleppo.
Moscow earlier said it had begun a "major operation" which saw the first missions carried out by warplanes taking off from the Admiral Kuznetsov aircraft carrier that was stationed off the Syrian last week.
The renewed offensive will be closely followed in Washington where President-elect Donald Trump has signalled he intends to take a different approach to Syria from that of President Barack Obama, who has backed some opposition groups.
Trump and Russian President Vladimir Putin, whose approach in Syria has been praised by the US president-elect, spoke by phone on Monday and agreed to "combine efforts to tackle international terrorism and extremism", the Kremlin said.