Syrian troops have launched fresh assaults on rebels, activists say, as an envoy of UN mediator Kofi Annan arrived in Damascus to discuss implementing a ceasefire plan.
Activists says several towns, including Homs, Deraa and the Douma suburb of Damascus, have been shelled.
There are also reports of a steep rise in refugees crossing into Turkey.
The UN Security Council is expected to adopt a statement urging Syria to carry out the plan "urgently and visibly".
It will call on Damascus to pull back its troops and heavy weapons from city centres, and for all parties including the opposition to cease armed violence w/n 48 hours of this pull-back.
A spokesman for Mr Annan said Syria had already reported some troop withdrawals. The UN expects a full truce by 12 April.
Meanwhile the International Committee of the Red Cross (ICRC) said that Syrian officials had agreed to it having an "expanded presence" in the country.
The UN says the conflict has cost more than 9,000 lives since it began a year ago. The Syrian government blames violence on "terrorist gangs" and says some 3,000 members of the security forces have been killed.
Foreign media face severe restrictions on reporting in Syria, and it is hard to verify the claims of either side.