United States Secretary of State John Kerry said that constant Russian bombardment has recently killed many civilians in Syria, demanding an immediate halt of Moscow’s air strikes which local opposition sources have said exceeded 100 sorties on a single day at times.
"Russia is using what are called free-fall bombs - dumb bombs," he told reporters at the State Department on Friday, indicating that "They are not precision bombs, and there are civilians, including women and children, being killed in large numbers as a consequence."
"This has to stop," he continued.
On Wednesday UN-mediated talks in Geneva to end the war in Syria were paused until Feb. 25. UN envoy Staffan de Mistura said they had not failed but urgently needed help from international backers led by the United States and Russia.
Meanwhile, Syrian regime forces and their allies have broken a three-year opposition siege on two towns in northwestern Syria, regime and opposition sources said on Wednesday, cutting off a main opposition route from Aleppo, the country's second largest city, to nearby Turkey.
Alongside heavy Russian aerial support, the advances have been made possible by advances by Hezbollah militants from Lebanon and Iranian-backed militant groups which support Bashar al Assad's regime.
The US and several western countries have blamed the Russian air campaign and regime attacks for the collapse of the Geneva peace talks which were aimed at securing "a broad ceasefire," according to UN special envoy Staffan De Mistura, to the five-year Syrian civil war which has killed more than 260,000 people.
"The Russians have made some constructive ideas about how a ceasefire could in fact be implemented, but if it's just talk for the sake of talk in order to continue the bombing, nobody's going to accept that. And we will know that in the course of the next days," Kerry noted.
He said the coming days would determine "whether or not people are serious, or people are not serious."
In addition, the Syrian regime’s recent advances near the northern city of Aleppo could worsen the country’s already dire humanitarian crisis, the White House said.
"Our principal concern about Aleppo right now is there's the possibility that government forces backed by the Russians would encircle that city and essentially lay siege to that city," White House spokesman Josh Earnest told reporters.
"That would obviously exacerbate a terrible humanitarian situation there," he underlined.
Earnest commented that "the more confident the Assad regime gets in terms of their hold on power, the less of an incentive they have to engage constructively in the political process."
While he wouldn’t rule out humanitarian aid drops for civilians, Earnest said that the US is focused "on trying to get the kind of cease-fire that would allow aid organizations to provide that relief and that assistance on the ground."
"You can move a lot more through a convoy of trucks than you can through pallets that are dropped out of a military transport aircraft," he pointed out.
On Thursday tens of thousands of Syrians reportedly flocked to the Turkish border north of Aleppo, following heavy Russian bombardment and reports that Syrian regime forces and its allies were making gains in Aleppo's northern countryside.
So far in the Syrian civil war at least 8 million people have been displaced internally while nearly 5 million have fled the country to the neighbouring countries of Turkey, Lebanon, Egypt and Jordan.