At least 16 people were killed as Syrian regime forces fired rockets in the outskirts of Damascus over Saturday and Sunday, according to the Syrian Observatory for Human Rights.
It was the biggest attack on the Qaboun area, to the city's northeast, in at least two years, a medical worker and the Observatory said.
The medical worker in nearby Eastern Ghouta, just outside Damascus, said he could hear explosions coming from Qaboun early on Sunday.
Violence in western Syria has increasingly tarnished a shaky ceasefire which took effect on December 30, backed by Syrian regime ally Russia and Turkey.
Syrian opposition ready for talks, but wants al-Assad's ouster
The Syrian opposition is fully committed to peace talks in Geneva on February 23, a senior official said on Sunday, but linked their readiness with the regime leader Bashar al-Assad's ouster.
"We are fully committed for the Geneva talks," Syrian National Coalition President Anas al-Abdah told delegates at the Munich Security Conference.
"We cannot address the profound security threats ... while Assad remains in power," he said.
UN envoy questions Trump's engagements in Syria
Addressing the Munich conference, UN envoy for Syria Staffan de Mistura on Sunday questioned US President Donald Trump's engagement in solving the Syrian conflict, days ahead of crucial peace talks in Geneva.
"Where is the US in all this? I can't tell you because I don't know," he said, adding that the new administration was still trying to work out its priorities on the issue.
The top three US priorities include fighting Daesh, "how to limit the influence of some major regional players and how to not to damage one of their major allies in the region," Mistura said. "How you square this circle, that I understand is what they are discussing in Washington," he said.
He said talks in Geneva would aim to see if there was a window for political negotiations to advance.
"Astana is the only place for the cessation of hostilities and Geneva is to see if there is any space for political discussion," Mistura said, referring to separate ceasefire talks in the Kazakh capital brokered by Turkey, Russia and Iran.
Turkey's Foreign Minister Mevlut Cavusoglu on Sunday called on the US and other allies to end their support for the PYD, which Turkey considers linked to the PKK, and instead support the moderate opposition forces in Syria. PKK is recognised as a terrorist organisation by the US, EU and Turkey.
"That is the mistake the previous administration in the US made. They gave weapons to the YPG and the PKK got some of the weapons. And PKK used those weapons in their terrorist attacks in Turkey," he said.
TRT World 's Simon McGregor-Wood brings more from Munich.