Russian warplanes and their Syrian government allies have continued an aerial assault on the separatist-held areas in Aleppo as rebels and aid workers accused them of destroying one of the city's main hospitals and killing at least two patients.
Meanwhile, Russia has cautioned the United States not to attack Syrian government forces because such a move would "lead to terrible, tectonic consequences not only" in Syria "but also in the region as a whole."
Russian Foreign Ministry spokeswoman Maria Zakharova also warned that regime change in Syria would leave a void that "terrorists of all stripes" would "quickly fill."
The blunt language comes with Washington weighing its options as Russian and Syrian Army forces continue stepped-up air strikes to support a ground offensive by embattled Syrian President Bashar al-Assad's forces against rebel-held areas of the northern city of Aleppo.
Those air strikes were blamed by an activist group that monitors the Syrian fighting for the barrel-bombing of one of Aleppo's largest hospitals, putting the facility out of service.
Separatist fighters and aid groups said at least seven bombs -- dropped by Syrian aircraft and Russian warplanes -- hit Sakhur hospital, Reuters reported.
The Syrian Observatory for Human Rights said on October 1 that at least two people were killed and at least 13 injured after the bombardment of the hospital by unidentified jets.
"The hospital is now out of service completely. There's destruction to walls, infrastructure, equipment, and generators. There are no more guards or staff left. It's complete darkness," said Muhammad Abu Rajab, who works as a radiologist in the hospital.
Meanwhile, the Gulf Cooperation Council (GCC) issued a demand on October 1 for the UN to intervene in Syria to stop aerial bombardments of Aleppo that it said had killed hundreds of civilians.
The Sunni Muslim-dominated council -- representing Saudi Arabia, the United Arab Emirates, Bahrain, Kuwait, Oman, and Qatar -- said the bombing by the Syrian government and its Russian ally was systematically destroying neighborhoods and was a "flagrant aggression contrary to international laws."
France has reportedly been working on a UN Security Council resolution for a cease-fire in Aleppo that would deem any country opposed to it to be complicit in war crimes.
U.S.-Russian tensions have escalated since the breakdown of a Syrian cease-fire late last month, with each side blaming the other for its failure.
The United States, Turkey, and their allies blame Assad for atrocities that include the use of chemical weapons against his own people, and have called for his removal and armed Syrian fighters to battle Assad's forces and the Islamist militant group Islamic State (IS), which controls swaths of Syria and Iraq.
Russia has waged a yearlong bombing campaign to keep longtime ally Assad in power and to fight groups that it regards as "international terrorists," including IS.
Russian Foreign Minister Sergei Lavrov on September 30 accused the United States and its allies on Syria of a refusal to distinguish between the anti-Assad opposition and terrorist groups, like the Al-Qaeda-aligned Al-Nusra Front.
"About the situation in Aleppo," Lavrov said, "the entire problem derives from the fact the United States and the coalition led by the United States cannot and refuses, basically, to separate the opposition from Nusra and the terrorist groups who joined Nusra."
Rebels and a monitoring group said on October 1 that the Russian and Syrian air strikes are focused on major supply lines into rebel-held areas and fighting rages in the Suleiman al-Halabi neighborhood, the front line to the north of Aleppo's Old City.
Rescue workers in the city said on September 30 that strikes on rebel-held residential areas included the use of incendiary and phosphorous bombs, causing extensive casualties, damage, and fires.
Doctors Without Borders on September 30 urged the Syrian government and its allies to "halt the indiscriminate bombing [in Aleppo] that has killed and wounded hundreds of civilians -- many of them children."
Meanwhile, The New York Times quoted U.S. Secretary of State John Kerry as telling antiregime Syrian representatives that he was "frustrated" after losing an argument within the Obama administration to back up diplomatic efforts to end the war in Syria with the threat of U.S. military force.
The newspaper cited an audio recording of a 40-minute discussion Kerry had with 20 or so participants at the Dutch mission to the United Nations on September 22, including representatives of four groups that provide education, rescue, and medical services in rebel-held areas of Syria, and diplomats from three or four countries.
Swedish Foreign Minister Margot Wallstrom issued a tweet on October 1 that echoed other Western criticism of the Russian and Syrian governments' actions in the conflict:
UN special envoy on Syria Staffan de Mistura this week called recent fighting some of "the worst...during the near six years of this devastating conflict" and said nearly 2 million people in Aleppo, Syria's largest city, are without running water.
The five-year conflict has killed more than 250,000 Syrians and displaced around half the country's prewar population, or around 11 million people.
In addition to Russia, Assad is also supported by Iranian ground forces and Shi'ite militia fighters from Lebanon and Iraq.
With reporting by AP and Reuters