In a statement, the High Negotiations Committee (HNC) also made its acceptance of the so-called "cessation of hostilities" conditional on the lifting of sieges and the delivery of humanitarian aid.
"The rebel factions agreed in principle on the possibility of reaching a temporary ceasefire provided it is done with international mediation and with guarantees obliging Russia, Iran and their sectarian militias and mercenaries to stop fighting," HNC chief Riad Hijab said in a statement.
After the talks fell apart, world powers last week proposed a ceasefire as part of a plan that also included expanded humanitarian access.
The truce was meant to have gone into effect by yesterday, but little progress has so far been made towards even a temporary halt to the fighting, which has only intensified in recent days.
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The statement, issued after a meeting of the HNC, said the opposition "wants to respond positively to international efforts to stop the Syrian bloodbath".
Regime backer Russia and opposition supporter Washington are meant to be co-chairing a UN panel that is working on the modalities of the temporary truce.
Officials from the two sides met for talks on the issue yesterday, but no official plan has been laid out, nor has a start date been proposed for a truce.
In recent days, fighting has intensified in Syria, particularly in northern Aleppo province, where rebel forces have lost ground to both regime forces backed by Russian air power and a Kurdish-led coalition called the Syrian Democratic Forces.
It now involves an array of groups including moderate and Islamist rebels, jihadists from Al-Qaeda affiliate Al-Nusra Front and the Islamic State group, the Kurds, and regime forces backed by Russia and Iran and Lebanon's Hezbollah movement.
More than 260,000 people have been killed in the conflict, and half the country's population has been displaced.