The United States has accused Russia and Syrian President Bashar al-Assad of waging a "concerted campaign" against civilians.
White House spokesman Josh Earnest said on September 26 that Syrian government forces, backed by Russian warplanes, were trying "to bomb civilians into submission."
His comments came after the Syrian government declared last week a new offensive against opposition rebels in eastern Aleppo, where some 275,000 people are living.
At least 231 civilians have been killed in violence in the embattled city and its outskirts since a weeklong cease-fire, brokered by the United States and Russia, fell apart on September 19, according to the British-based Syrian Observatory for Human Rights.
U.S. Secretary of State John Kerry said on September 26 that the Syrian and Russian governments "seem intent on taking Aleppo and destroying it in the process."
Moscow has blamed Washington for the escalating violence, saying moderate opposition groups funded by the West violated the cease-fire and had failed to cut their ties with extremists.
Based on reporting by AP and dpa