The Unitied Nations envoy Staffan de Mistura also warned that 23 buses and Syrian drivers had been stopped by armed groups from assisting in evacuations from two villages in Idlib province.
Responding to the news, World Vision UK said: "We are continuing to provide food and blankets for those in need."
Speaking to reporters in Geneva on Thursday, de Mistura said the ceasefire negotiated by Russia and Turkey last month was being upheld in most places, however, some violence has continued in the Wadi Barada valley.
The UN officials was quoted by Reuters as saying: "Military activities in that area means also the potential of further damaging water pumps and water supplies."
De Mistura also told journalists he believes the United Nations will be invited to talks in Kazakhstan on 23rd January aimed at strengthening the ceasefire before UN talks in February.
According to the UNHCR, more than 4.8 million Syrians are currently registered as refugees amid the country's ongoing civil war.