Syrian and rebel forces continued to clash Saturday in the besieged city of Aleppo, where some 250,000 people, including many children, remain trapped.
Syrian forces have been moving to retake parts of Aleppo run by rebels, who fire on government-controlled sections of the city. Casualties continue to mount on both sides.
The World Health Organization (WHO) has called for the immediate evacuation of hundreds of sick and wounded people from eastern Aleppo.
The WHO estimates children comprise about one-third of the hundreds of civilians killed and wounded over the past two weeks.
“The situation really is unfathomable," said Rick Brennan, WHO director of humanitarian emergencies. "According to health officials there, there have been 338 deaths in the last couple of weeks due to the bombardment, including 106 children. Eight-hundred-and-forty-six other individuals have been injured, again almost a third children - 261 children.”
U.S. President Barack Obama has strongly condemned the "barbarous Russian and Syrian regime airstrikes" on civilians in eastern Aleppo.
The White House says Obama spoke by telephone Thursday with German Chancellor Angela Merkel. Both agreed that Russia and the regime of Syrian President Bashar al-Assad bear a "special responsibility" for stopping the fighting and letting in humanitarian aid.
Secretary of State John Kerry said earlier the United States is "on the verge" of suspending diplomatic talks with Russia because of Moscow's continued bombing of rebels in eastern Aleppo.
A monitoring group said Friday Russian airstrikes across the country in the past year have killed more than 9,000 people, including many civilians. The Britain-based Syrian Observatory for Human Rights said many more civilians were wounded by the airstrikes.
Kerry called it “irrational” to keep talking and “take things seriously” after Russia vowed to continue the airstrikes.
“It’s one of those moments where we’re going to have to pursue other alternatives for a period of time,” said Kerry. He added he is “extremely concerned” about the future of the Syrian people.
Kerry's spokesman told reporters the State Department is in "active" contact with the Kremlin, but is still prepared to step away "barring some significant steps by Russia."
"We are still prepared to enact that kind of a suspension and we're in consultations right now inside our own government, and of course, with [Russian] Foreign Minister [Sergei] Lavrov,” John Kirby said Thursday.
The United States is pushing Russia to pressure its close ally, President Assad, to honor a cease-fire and let U.N. relief convoys into Aleppo.
Russia and the Syrians say they are targeting "terrorists" - their term for the rebels aiming to topple the Syrian government.
The U.S. says Russia and Syria are hitting hospitals, refugee camps and such critical sites as water and power plants. The U.S. says the bombs are indiscriminate and that the Russians make no effort to specifically hit their stated target - Islamic State fighters.
U.N. humanitarian aid chief Stephen O'Brien told the U.N. Security Council Thursday that what is happening in Aleppo fills him with "raw grief, dismay, intense sadness, frustration and an unquenchable anger."
"Besiegement is not a weapon of war. It is a flagrant, unjustifiable breach of the law. One day there will be no hiding place for the individuals and institutions callously, cynically perpetrating these war crimes."
O'Brien also had harsh words for U.N. diplomats for their perceived inaction in Syria.
"The only remaining deterrent it seems is that there will be real accountability in the court of world opinion and disgust. Goodness knows, nothing else seems to be working to stop this deliberate and gratuitous carnage."
U.N. Secretary-General Ban Ki-moon Friday announced an investigation into an incident on September 19 involving a relief operation by the U.N. and the Syrian Arab Red Crescent. Humanitarians came under fire in Urum al-Kubra, when 31 trucks were delivering life-saving assistance, leaving at least 18 people dead.
The White House has said President Obama keeps pressing his security team to come up with better options in Syria.
Russia said it supports a 48-hour cease-fire in Aleppo, but not a longer truce proposed by the U.S.
Kremlin spokesman Dmitry Peskov insisted Moscow still wants to reach a deal to renew the September 9 cease-fire, but said, "We have unfortunately taken note of the rather unconstructive character of the rhetoric from Washington over the past few days."
The United Nations calls the plight of Aleppo desperate. Officials say medical evacuations are needed and food stocks are running low.
VOA's Mary Alice Salinas contributed to this report from the White House, Lisa Schlein - from Geneva.