The Syrian National Coalition, the main Western-backed opposition group, says indiscriminate Russian aerial attacks are now the leading killer of civilians.

Najib Ghadbian, the coalition's U.N. representative, said Russia's intervention in Syria is facilitating President Bashar Assad's "war on civilians" and elimination of moderate opposition forces — contrary to Moscow's claim that its campaign is aimed at countering "terrorist extremist groups."

Ghadbian said in a letter to the U.N. Security Council on Monday that Russia has carried out more than 297 airstrikes since initiating its campaign on Sept. 30.

According to data from Syrian Civil Defense rescue workers, he said, more than 436 civilians have been killed since then and "more than half of these civilian deaths are directly attributable to Russian airstrikes."