The U.N. special envoy to Syria will travel to Damascus this month to pursue a start date for a proposed six-week suspension of government airstrikes and artillery shelling in the city of Aleppo, a new report says.

Staffan de Mistura this week announced the Syria government's willingness to try his plan to freeze hostilities in Syria's largest city, though it's not known whether opposition forces will agree to it.

The latest report by Secretary-General Ban Ki-moon on Syria's humanitarian crisis, released Friday, says de Mistura will send a team to Aleppo by the end of this month to assess the conditions for the freeze, "following which he expects to be able to announce when the beginning of the six weeks will come into effect."

The report says de Mistura will press the opposition to "do their part" and avoid the use of heavy weapons, including rockets and mortars, in Aleppo during the six-week period.

The proposed pause in hostilities in the northern city is meant to allow the U.N. to experiment with delivering humanitarian aid to Salaheddine, a densely populated and contested area in central Aleppo. If the test is successful, de Mistura envisions expanding the approach to other areas.

In support, Ban on Friday called for an immediate de-escalation of the conflict in Syria to give civilians relief and to allow a step toward a political solution of the four-year conflict.

A statement released by Ban's spokesman urges opposition forces to suspend their shelling of Aleppo to allow the freeze to be tested.

De Mistura has said he wants to start with Aleppo because it has symbolic value as Syria's diverse commercial capital and because it has the country's highest number of displaced people.

The city has been carved in two since opposition fighters launched an assault in mid-2012, leaving the eastern half in rebel hands and the western half with the government. Whole neighborhoods are in rubble, and opposition fighters face a two-front war against the government and the Islamic State group.

The overall conflict in Syria has killed at least 220,000 people and sent more than 3.8 million people fleeing the country.