Government jets bombed suburbs in Damascus and a car bomb killed 10 people in the capital on the last day of a four-day truce in Syria.
Each side blames the other for breaching the truce arranged for the Muslim holiday of Eid al-Adha, by the United Nations - Arab League envoy Lakhdar Brahimi, Reuters reports.
UN Secretary-General Ban Ki-moon said he is deeply disappointed they failed to respect the call to suspend fighting. He said the crisis cannot be solved with more weapons and bloodshed.
Meanwhile, Mr Brahimi said he will not let the failure discourage him.
"We think this civil war must end ... and the new Syria has to be built by all its sons," he said. "The support of Russia and other members of the Security Council is indispensable."
But after meeting Russian Foreign Minister Sergei Lavrov in Moscow, Mr Brahimi said there is no immediate plan to send UN peacekeepers to Syria. He will next go to Beijing.