Millions of people living in the rebel-held region, several of whom fled the rule of President Bashar al-Assad, will be affected if the UN fails to resume humanitarian aid there.
The United Nations Office for the Coordination of Humanitarian Affairs (OCHA) on Friday said it was concerned the Syrian government has imposed "unacceptable conditions" on the delivery of humanitarian aid to the northwest of the country.
Aid delivery operations through the crossing between Turkey and Syria has been stalled since Monday, when a 2014 UN deal expired.