Syrian rebel groups have confirmed that they will attend peace talks with the government in Kazakhstan next week.
A leader of Jaysh al-Islam, Mohammed Alloush, said he would head the rebel delegation and aim to end the "crimes" of the government and its allies.
The talks in Astana are being organised by Russia and Turkey.
The two countries, which back opposing sides in the civil war, brokered a truce on 30 December that has been threatened by repeated violations.
Air strikes and clashes have been reported on several battlefronts, particularly in the Wadi Barada region north-west of Damascus.
On Sunday, at least nine civilians were killed by government shelling of a rebel-held village there, according to the UK-based Syrian Observatory for Human Rights.
The truce excludes the jihadist groups Islamic State (IS) and Jabhat Fateh al-Sham, known as al-Nusra Front until it broke off formal ties with al-Qaeda in July.
Rebel factions took the decision to send a delegation led by Mr Alloush to the talks in Astana at a meeting in Turkey on Monday.
"All the rebel groups are going. Everyone has agreed," Mr Alloush, the head of the political office of Jaysh al-Islam, told AFP news agency.
"Astana is a process to end the bloodletting by the regime and its allies. We want to end this series of crimes," he added.
An official in the Free Syrian Army, under whose banner a number of Western-backed groups fight, told Reuters: "The factions will go and the first thing they will discuss will be the matter of the ceasefire and the violations by the regime."
Earlier, the pro-opposition Shaam News Network reported that several rebel groups wanted to boycott the talks because of the government's offensive on Wadi Barada.
The delegation travelling to Astana will be different to the one sent to UN-brokered peace talks in Geneva a year ago by the main umbrella group representing Syria's political and armed opposition factions, the High Negotiations Committee.
Mr Alloush quit as the HNC's chief negotiator in May, saying the Geneva talks had been "a waste of time" and accusing the government of intransigence.
The HNC issued a statement on Saturday stressing its "support for the military delegation" travelling to Kazakhstan and expressing its "hope that this meeting will reinforce the truce".
It added that it considered the Astana meeting a "preliminary step for the next round" of negotiations on a political settlement in Geneva.
Russia has said they will complement rather than compete with the Geneva talks.
President Bashar al-Assad has been quoted as telling French politicians that he is "optimistic" about next week's meeting and is "ready for reconciliation with [the rebels] on the condition that they lay down their arms".
The initiative by Moscow and Ankara follows a significant defeat for the rebels in the battle for the northern city of Aleppo, which government forces retook on 22 December with the help of Russian air strikes and Iranian-backed militiamen.
More than 300,000 people have been killed and 11 million others displaced in almost six years of conflict, which began with anti-government protests before escalating into a full-scale civil war.