U.N. second in command Jan Eliasson said on Monday he was discussing with Turkish officials whether they can open the border to the thousands fleeing fighting in Aleppo in case the violence reaches where they are huddled on the Syrian side.

Close to 100,000 people are locked out of Turkey near the Oncupinar border crossing after they fled escalating airstrikes and a Syrian government assault on Aleppo, with humanitarian aid from Turkish relief agencies provided inside Syria.

Turkish President Tayyip Erdogan has repeatedly said he prefers the setting up of a "safe zone" perimeter inside Syria border where displaced people would be protected from attack.