Diplomats say Russia has objected to a proposed U.N. Security Council statement expressing outrage at Syrian government airstrikes, especially this week's indiscriminate use of heavy weapons in Aleppo that have killed more than 100 people.

The proposed council statement required approval from all 15 members.

Diplomats said Russia, the Syrian government's most important ally, wanted all references to the regime stripped from the statement, so the U.S. decided to drop it.

Russia and China have vetoed three Western-backed resolutions that would have pressured President Bashar Assad to end the violence.

Kurtis Cooper, spokesman for the U.S. Mission, said Thursday the U.S. is "very disappointed that a Security Council statement expressing our collective outrage at the brutal and indiscriminant tactics employed by the Syrian regime against civilians has been blocked."