The returnees struggle with a "lack of basic services, limited transportation, and largely destroyed public infrastructure," UNRWA said. Some live in houses without doors or windows.
At least a hundred people were killed strikes by Syrian air and ground forces on rebel-held areas across Syria, in the deadliest single-aerial attack by government forces since November 25.
Beji Caid Essebsi tops presidential elections poll, but short of the 50 percent threshold required to win outright. A polarising battle is expected between him and Marzouki ahead of the second round set for 28 December.
Deadline looms for a deal between Iran and world powers over Tehran's nuclear programme and international sanctions. Lavrov arrives in Vienna for frenzy of last-minute talks, as Tehran says willing to extend negotiations by up to a year.