The United States is accusing Russia and its ally, the government of Syrian President Bashar al-Assad, of conducting a "concerted campaign ... to bomb civilians into submission" in the war-torn country.
Josh Earnest, spokesman for US President Barack Obama, on Monday cited the latest reports of strikes on civilians, including water supplies in eastern Aleppo.
"The idea of weaponizing access to a clean water supply for civilians is beyond the pale," Earnest said. "People of good conscience around the world should speak up and are speaking up."
Fresh airstrikes took place overnight in eastern Aleppo, activists said earlier Monday, inflicting more fatalities as the Syrian government offensive to retake the rebel-held part of the city showed no signs of relenting.
The government's airstrikes have been strongly condemned by Western nations who have also been sharply critical of Russia. Moscow is carrying out its own aerial raids to back pro-government forces.
Yassen Abu Raed, an activist in eastern Aleppo, said at least 10 people, among them children, have been killed in the morning raids.
In Moscow, Kremlin spokesman Dmitry Peskov complained about the "unacceptable" tone of "rhetoric" from British and US officials.
"We believe that such rhetoric can cause great harm to the settlement process and our bilateral relations," he said earlier, according to the TASS news agency.
Peskov was responding to comments Sunday at the United Nations by the US and British ambassadors.
Matthew Rycroft, British ambassador to the UN, had said in New York that Russian actions "have prolonged the conflict, prolonged the suffering." Samantha Power, US ambassador to the UN, had said that Russia and al-Assad were making war "instead of pursuing peace."
More than 237 people, including at least 38 children, have been killed in the week since a US-Russia brokered ceasefire collapsed and the Syrian government and its allies, including Moscow, resumed heavy airstrikes, the Syrian Observatory for Human Rights said.
"The raids are targeting every single neighbourhood in eastern Aleppo on Monday," activist Bahaa al Halabi told dpa. "The situation is catastrophic."
The raids appear aimed at weakening the rebels' positions and allowing pro-government forces to eventually stage a full scale ground assault on the eastern areas.
Earnest said that Obama is "deeply concerned" about the latest violence in Syria.
"The situation has been terrible, and the bloodshed sickening, but we've seen that over the weekend it just got worse," Earnest said.
Eastern Aleppo has been under siege since July and residents report declining supplies of basic goods, including food and medicine. Water supplies have also been badly damaged.
The high number of casualties, including many hundreds of injured people, have strained already depleted hospitals and makeshift medical centres, many of which have been bombed during the war.