Ban said despite the Syrian government's agreement to cease all violence, there is still "deeply troubling evidence" that the situation on the ground has not changed.
"The situation (in Syria) remains highly precarious... Despite assurances from the government, there has been no meaningful progress on the ground. This is unacceptable," Ban told reporters here.
Ban said he has recommended that the UN Security Council authorise the establishment of an UN supervision mission in Syria, comprising up to 300 military observers supported by a civilian component.
"This is not a decision without risk. But I believe it can contribute to achieving a just peace and political settlement, reflecting the people's will in Syria," the UN Chief said.
The Security Council had on Saturday authorised the deployment of an advance team of 30 unarmed military observers to liaise with the parties and to begin to report on the implementation of a full cessation of armed violence, pending the deployment of a UN supervision mission that will be tasked with monitoring the cessation.
The first group of the UN military monitors arrived in Damascus earlier this week.
Ban's remarks came even as the UN and the Syrian government concluded an agreement in Damascus for a preliminary protocol outlining the functions of the observer mission and the tasks and responsibilities of the Syrian government in this regard.