Government tanks have shelled two suburbs of the Syrian capital Damascus, opposition activists say.
The military assault on Hasrata and Irbin began in the early hours of the morning, after rebels attacked a government intelligence compound, they said.
There are reports of army offensives in other parts of Syria.
UN Secretary General Ban Ki-moon warned of serious repercussions if the crisis in Syria is not resolved.
Speaking at a conference in Indonesia he warned the world could not afford to look away.
“We all have a responsibility to work for a resolution of this profound and extremely dangerous situation, a crisis that has potentially massive repercussions for the region and the world,” he said.
The UN Security Council is due to meet in New York to try to agree a statement on a peace plan put forward by UN and Arab League special envoy Kofi Annan.
Video at last above tweet.