A rocket and mortar barrage struck a government-controlled neighborhood in Syria's northern city of Aleppo on Sunday, killing 13 civilians and wounding 40, the government and an opposition group was quoted by ABC News as saying.
State-run news agency SANA said the attack by "terrorists" occurred in the predominantly Kurdish neighborhood of Sheikh Maqsoud, which has been subjected to insurgent shelling for days despite a shaky US and Russian-brokered cease-fire that took effect Feb. 27.
The Syrian Observatory for Human Rights, a Britain-based opposition group that monitors the conflict, said more than 70 rockets and mortar shells were fired at Sheikh Maqsoud and reported nine civilians killed, including four children, and 30 wounded.
The Observatory said the shells were fired by insurgents, including the al-Qaida branch in Syria known as the Nusra Front. That group and its rival, the Islamic State group, are excluded from the cease-fire.
The cease-fire has brought a sharp drop in violence to much of Syria and has largely held despite sporadic violations and mutual accusations of breaches. The US and Russia are now looking to convince the two sides to return to UN-brokered peace negotiations in Geneva next week.
In a telephone conversation Sunday, Russian Foreign Minister Sergey Lavrov and U.S. Secretary of State John Kerry gave "an overall positive assessment of the progress toward securing the cease-fire in Syria, which is being generally observed and already has led to a sharp decrease in the level of violence," the Russian Foreign Ministry said in a statement.
Although much less aid than anticipated has gone into besieged areas since the cease-fire started, the diplomats noted "significant improvement" in humanitarian access.
They stressed the need to avoid delaying the start of the Geneva negotiations.