Russia has said its air force will continue to target the Syrian regime's enemies and brushed off US warnings as "clumsy." Washington had called on Moscow to ground its planes to help restart a ceasefire.
The Kremlin said Thursday that Russian warplanes would press ahead with its operations in Syria and dismissed a US warning of potential blowback against Russia.
Kremlin spokesman Dmitry Peskov urged Washington to deliver on a pledge to separate moderate Syrian opposition fighters from "terrorists."
The US had raised hackles in Moscow after US State Department spokesman John Kirby said Wednesday that Russia has an interest in stopping the violence in Syria because militants could exploit the vacuum there and launch attacks "against Russian interests, perhaps even Russian cities."
Officials in Washington are reportedly mulling tougher responses to the Russian-backed Syrian government assault on Aleppo, including military options, as rising tensions with Moscow diminish hopes for a diplomatic solution.
The escalating violence in the multi-lateral Syrian civil war is leading to increasingly pessimistic assessments from those charged with cheerleading for a new truce.
"At the moment, when bombs are falling all over, it is very difficult to justify resuming talks," the UN special envoy to Syria, Staffan de Mistura, told the AFP news agency after he met Pope Francis at the Vatican.
This comes despite friendly noises from Turkey - a major backer of anti-Syrian regime rebels - which has been making conciliatory gestures trying to restart the truce.
"We have to try harder for a ceasefire and political resolution," Turkish Foreign Minister Mevlut Cavusoglu told reporters in Ankara following talks with his Iranian counterpart, another key ally of Damascus.
"If Russia is prepared to cooperate with us on the ceasefire and humanitarian aid, we are more than ready," Cavusoglu added.
The only recent hope is a statement from Russia's foreign ministry that said that while a seven-day ceasefire plan proposed by Washington was unacceptable, the Kremlin was open to a 48-hour "humanitarian pause" in Aleppo to ease humanitarian suffering there.
This comes as unidentified jets bombarded bakeries in two rebel-held areas in Syria's northern province of Aleppo, activists said Thursday. "One bakery was bombed in the town of Anadan in the northern countryside of Aleppo and a second was struck in the town of Kfar Naha in the western part of Aleppo countryside," a local activist, who gave his name only as Wissam, told the DPA news agency. Unconfirmed reports said at least three people were injured in the second raid.
The Syrian Observatory for Human Rights, a UK-based monitoring group, reported aerial strikes on both areas.
jar/bc (Reuters, AFP, dpa)