The Syrian opposition said on Friday armed groups fighting President Bashar al-Assad would respect a two-week week truce beginning at midnight, but said the government and its allies must not launch attacks on the pretext of fighting terrorism.
"The High Negotiations Committee confirms the agreement of the Free Syrian Army factions and the armed opposition to a temporary truce from midnight Saturday," an HNC statement said.
The HNC said the government and its allies must not use the "proposed text to continue the hostile operations against the opposition factions under the excuse of fighting terrorism".
Heavy air strikes were reported to have hit rebel-held areas near Damascus as fighting raged across much of western Syria on Friday, hours before a US-Russian plan aimed at halting hostilities was due to take effect.
The "cessation of hostilities" agreement is due to take effect at midnight (2200 GMT on Friday).
The government has agreed to the plan. The main opposition alliance, which has deep reservations about the terms, has said it is ready for a two-week truce to test the intentions of the government and its Russian and Iranian backers.
The Syrian Observatory for Human Rights monitoring organisation reported at least 26 air raids and artillery shelling targeting the town of Douma in rebel-held Eastern Ghouta near
Damascus. Rescue workers in the opposition-held area said five people were killed in Douma, listing their names on their Twitter feed. Syrian military officials could not immediately be reached for comment.