Air strikes pounded Aleppo province while at least 11 civilians, including seven children, died during attacks on the city of Idlib, nearby Jarjanaz and central Hama province, the Syrian Observatory for Human Rights said.
With no let-up in the military campaign, US Secretary of State John Kerry admitted that months of diplomacy to end the war had hit a dead-end.
"I think we are on the verge of suspending the discussion because, you know, it's irrational in the context of the kind of bombing taking place, to be sitting there, trying to take things seriously," he told a conference in the US capital.
Syria's ally Russia said it would press ahead with the air war in support of the regime, warning that Washington's refusal to work with Moscow on a settlement would be a "gift to terrorists."
"If Washington's threats to halt cooperation become concrete decisions, then there is no longer any doubt that the rebels are under the White House's protection and in the streets, terrorists will celebrate," Russian foreign ministry spokesman Maria Zakharova said.
Russia and the United States have traded blame for last week's collapse of a ceasefire deal that would have marked the first step in a new effort to end the war that has killed 300,000 people since 2011.
Aleppo's descent into abyss
International alarm is growing over the crisis in rebel-held eastern Aleppo, where the Syrian army launched an offensive a week ago to retake the city.
UN aid chief Stephen O'Brien told the Security Council in New York that Aleppo is descending into a "merciless abyss of a humanitarian catastrophe unlike any we have witnessed so far in Syria."
More than 100,000 children remain trapped in east Aleppo, which has come under intense bombing since the Syrian army offensive began, he said.
The siege by Syrian government forces has made food scarce and fresh water in short supply, he added, and there are mounting reports of deaths from malnutrition, disease and poisoning by those scavenging for food.
US Ambassador Samantha Power described the escalation as "the most savage week we've seen in an incredibly savage five-plus-year war," with more than 1,000 people killed by 1,700 air strikes on rebel-held east Aleppo alone.
France said it would push for a UN resolution to impose a ceasefire in Aleppo, but it remains unlikely that Russia would support such a measure.
Moscow maintains that a US-led coalition strike on a Syrian army base, on top of Washington's failure to rein in opposition rebel fighters, led to the collapse of the truce.
Bombs are falling
Kerry said the United States would pursue other alternatives, "barring some clear indication by the warring parties that they are prepared to consider how to approach this more effectively."
The UN envoy for Syria, meanwhile, said there was little prospect of an imminent restart of any negotiations to try to end the raging conflict as the violence continues.
"At the moment, when bombs are falling all over, it is very difficult to justify resuming talks," Staffan de Mistura told AFP after meeting Pope Francis at the Vatican.
In a sign of the desperate plight facing residents of eastern Aleppo, the United Nations warned that hundreds of people probably need medical evacuation.
Two of the largest hospitals in the city's east were bombed on Wednesday in what UN Secretary General Ban Ki-moon described as a war crime.
Share
