BEIRUT — Syrian rebels launched a broad offensive for Aleppo on Friday as the Russian, Syrian, and Iranian foreign ministers vowed to intensify their fight against terrorism in the country.

The battlefield allies met in Moscow as the Syrian government is looking to cement its authority over the divided northern city and the contested suburbs of the capital, Damascus.

Fighting for Aleppo appeared to have calmed by the afternoon after rebels assaulted the city’s government-controlled western side with three vehicle bombs and at least 150 rockets in the morning. The Syrian military said the rockets were Russian-made Grad missiles.

At least 15 civilians were killed in the volley, according to pro-government TV stations. The Britain-based Syrian Observatory for Human Rights monitoring group also said that 15 civilians were killed, and over 100 injured.

A reporter inside the city for the Lebanon-based Al-Mayadeen TV channel had reported attacks on “all sides” of the city, “from the farthest points north to the farthest south.”

Rebels said they seized a factory and pushed into government-held neighborhoods in southwestern Aleppo, but the Syrian military said through SANA that it had repelled the offensive from all fronts, with support from allied militias.

“The Syrian army and its allies are in control on the ground and armed groups were not able to change the map,” the military statement said. “Fighting is still ongoing but the intensity has dropped.”

This is the second attempt by rebels to break the government’s siege of Aleppo’s opposition-held eastern districts, where the U.N. estimates 275,000 people are trapped. U.N. Special Envoy Staffan De Mistura has estimated 8,000 of them are rebel fighters, and no more than 900 of them are affiliated with the al-Qaida-linked Fatah al-Sham Front.

The area has been subjected to a ferocious campaign of aerial attacks by Russian and Syrian government warplanes, and hundreds of people have been killed in recent weeks, according to opposition activists and trapped residents.