U.S. Secretary of State John Kerry said Washington was on the verge of suspending talks with Russia on a cease-fire agreement in Syria, as a devastating bombardment of the city of Aleppo by Russian and Syrian warplanes continued.
Kerry’s comments on September 29 came hours after the Kremlin dismissed U.S. threats to suspend cooperation with Moscow in Syria and said Russian forces would continue to support a government offensive on rebel-held neighborhoods of Aleppo.
U.S. President Barack Obama and German Chancellor Angela Merkel during a phone call on September 29 condemned what they called "barbarous" Russia and Syrian air strikes on Aleppo, noting that the city is "populated with hundreds of thousands of civilians, half of whom are children," the White House said.
Two of the largest hospitals in the city's east were bombed earlier in the day in what United Nations Secretary-General Ban Ki-moon described as a "war crime."
Obama and Merkel agreed that Russia "bears special responsibility for ending the fighting in Syria and granting the UN humanitarian access to besieged and hard-to-reach areas in Syria," the White House said.
The U.S. State Department, meanwhile, confirmed that Kerry spoke by telephone with Russian Foreign Minister Sergei Lavrov on September 29 about the "fragility" of the situation in Syria. Lavrov said that he will hold another telephone conversation with Kerry on September 30 to discuss separating Syria's moderate opposition from the Al-Qaeda-linked group formerly known as the Al-Nusra Front.
Russian news agencies quote Lavrov as also saying that a cease-fire deal on Syria that Moscow agreed with Washington was still working. He additionally said Russia was not using banned weapons in Syria and demanded evidence from those accusing Moscow of hitting civilian targets.
A U.S. spokesman said Washington was "very serious" about the potential of suspending its arrangement with Russia on Syria unless "significant steps" are taken by Moscow.
But Russia shot back on September 29, with Moscow's Foreign Ministry saying U.S. refusal to cooperate with Russia on Syria would be a gift to "terrorists."
Ministry spokeswoman Maria Zakharova said on Facebook that if Washington follows up on its threat to cut off cooperation, it would mean that "the White House has taken the militants under its wing." She added it would make the best possible "present to terrorists."
Washington and Russia had been negotiating for months over the potential terms of a lasting cease-fire in Syria. The latest truce collapsed on September 19 after several days of calm.
Aleppo, once Syria's largest city, has suffered from intensive air strikes since September 19.
WATCH: With Aleppo In Tatters, U.S. Calls Russian Air Strikes 'Barbarism'
Kerry told a conference in Washington on September 29 that the ongoing bombing campaign amounted to war crimes.
"We are on the verge of suspending the discussion because it is irrational in the context of the kind of bombing taking place to be sitting there trying to take things seriously," Kerry said.
"It is one of those moments where we are going to have to pursue other alternatives," he said.
Earlier, Russia’s Deputy Foreign Minister Sergei Ryabkov dismissed a warning from Washington about the attacks that have killed hundreds of civilians in Aleppo as an "emotional outburst" and also said it was tantamount to supporting terrorism.
Ryabkov rejected Washington's calls for a seven-day pause in the Aleppo offensive as "unacceptable," saying it would give militants time to regroup.
Kremlin spokesman Dmitry Peskov also described the State Department remarks as awkward and said the "war on terror" in Syria would continue.
In his September 29 speech, Kerry did not specify any new approach for bringing peace to Syria.
Kerry also said it was unlikely that the United States would go to war in Syria.
Obama had said on September 28 that it was important to be "judicious" in sending troops to Syria because of the "incredible sacrifices" involved and also because the U.S. military remains involved in Afghanistan and Iraq.
"There are going to be some bad things that happen around the world, and we have to be judicious," he said at a military base in Virginia. Yet, "in Syria, there is not a scenario in which -- absent us deploying large numbers of troops -- we can stop a civil war in which both sides are deeply dug in."
Earlier in the day, Merkel said after phone consultations with Turkish President Recep Tayyip Erdogan that Russia has a "special responsibility to calm violence and give a political process a chance" in Syria.
Merkel's office said she and Erdogan agreed that "repeated flagrant violations against humanitarian international law" in Aleppo are "unacceptable" and that "a cease-fire is more urgent than ever."