Damascus (AFP) - The UN's peace envoy for Syria Staffan De Mistura was making a surprise visit to Damascus on Monday, a government source told AFP, as world powers push for a ceasefire this week.

The source, who spoke on condition of anonymity, said De Mistura was expected to arrive later Monday and meet Foreign Minister Walid al-Muallem on Tuesday.

The envoy's visit comes after world powers last Friday called for immediate aid access throughout Syria and a "cessation of hostilities" to begin within a week.

The plan was intended to help pave the way for the resumption of peace talks presided over by De Mistura that collapsed earlier this month.

The source said the envoy was expected to discuss the ceasefire and aid access plan, as well as the possible resumption of talks on February 25.

He said it was not yet clear how long De Mistura would be in the country.

Earlier, the envoy's office had announced that a press conference scheduled for Tuesday in Geneva was being pushed back to Friday, without giving a reason.