BEIRUT — Government bombardment of rebel-held neighborhoods in Aleppo killed at least 20 people Saturday, the worst since airstrikes resumed Tuesday, said Syrian opposition activists, as the U.S. called for an end to the bombings.

Saturday was the fifth day of renewed assaults by Syrian warplanes on eastern Aleppo districts, a rebel-held enclave of 275,000 people. The onslaught began Tuesday, when Syria's ally Russia announced its own offensive on the northern rebel-controlled Idlib province and Homs province in central Syria.

—Staff and news services