Fighters from the al-Qaeda-affiliated Nusra Front (pictured) have been among those besieging Fuaa and Kefraya
The Lebanese Shia militia Hezbollah has confirmed a six-month truce in fighting against anti-government rebels in two areas of Syria.
Hezbollah's leader, Hassan Nasrallah, said the truce would cover the town of Zabadani, near the Lebanese border, and two Shia towns in the north-east.
He said the deal was reached under UN auspices and with Iranian mediation.
Hezbollah has long been fighting alongside President Assad's forces to secure the Syrian border with Lebanon.
The deal will see anti-Assad fighters allowed to withdraw from Zabadani, which been under siege from pro-government forces backed by Hezbollah.
In July, the UN envoy for Syria said government barrel-bomb attacks on Zabadani had caused "unprecedented levels of destruction and many deaths among the civilian population".
In return, the rebels will allow the evacuation of thousands of civilians from the two Shia villages of Kefraya and Fuaa, which have been under rebel siege in Idlib province.
Zabadani is the last major rebel stronghold along the Lebanese border. Rebel fighters have just about been holding out, but have faced almost certain defeat.
A similar situation has developed around Kefraya and Fuaa, but in reverse - the rest of Idlib province has all but fallen to a rebel alliance, the Army of Conquest.
Last month 48-hour ceasefires were agreed to allow food and medical supplies into the two areas.
The new agreement means that for once a bloody end to two battlefronts in Syria may be avoided while both sides will feel they have achieved useful territorial gains, says the BBC's Arab affairs analyst Sebastian Usher.
Localised ceasefires have occasionally been reached elsewhere in Syria, our correspondent adds.
At one point they were proposed as one of the few ways out of the bloodshed and stalemate - but they have failed to build any real momentum, he says.
