Syria's military says it will adhere to a four-day ceasefire, beginning Friday, for the Muslim holiday of Eid al-Adha.
The truce - proposed by the international envoy Lakhdar Brahimi, who hopes it will lead to a peace process - was due to begin at 4pm Friday NZ time.
Reporting the announcement, Syrian state television added: "Syrian armed forces will, however, reserve the right to reply to terrorists attacks, attempts of armed groups to reinforce or resupply, or attempts to infiltrate from neighbouring countries."
Qassem Saadeddine, a spokesperson for the joint command of the Free Syrian Army, the main armed rebel group, says they will back the truce but will not allow the regime to reinforce its posts.
The BBC reports that the news came as rebels said they had advanced into several central areas in Aleppo, Syria's largest city and a key battleground in recent months.
Previous attempts at ceasefires in Syria have collapsed, and the violence has continued to escalate.
The United States welcomed the ceasefire, and United Nations Secretary-General Ban Ki-moon says he hopes it will lead to political negotiations.
UN aid agencies have geared up to take advantage of any window of opportunity provided by the ceasefire and plan go to areas that have been difficult to reach because of the fighting.
The refugee agency UNHCR says it has prepared emergency kits for distribution to up to 13,000 families in previously inaccessible areas, including the cities of Homs and Hassaka.