The United Nations refugee agency said on Friday that for the first time it had reached the opposition-held Azaz area of northern Syria where it found an estimated 45,000 displaced people living in appalling conditions in makeshift camps.

"This is an area that the UN has not been able to physically reach ever since the beginning of the conflict," Yacoub El Hillo, director of UNHCR's Middle East and North Africa Bureau, told reporters in Geneva.

Azaz is located opposite Kilis camp on the Turkish side that holds about 10,000 Syrian refugees who have crossed that border, according to the UN High Commissioner for Refugees (UNHCR).

"On this (Syrian) side it is makeshift camps in appalling conditions. So hopefully this will be the first of many, many convoys that we will be operating," El Hillo said.

The Syrian government does not allow UN agencies to enter rebel-held areas from across its borders, but aid agencies, including Medecins Sans Frontieres, have been active in the Azaz region where temperatures are now sub-zero, he said.

"They want us to continue, it could not have happened without the Syrian government. For the planes to land near Latakia we had to have landing permits and also for the trucks to move," El Hillo said.