Staffan de Mistura made his comments in Jordan after meeting Minister of Foreign Affairs Ayman Safadi who said that Jordan's "firm position" is that a political solution must be found, and "destruction and killing must be stopped in order for Syria to be recovered and to restore its role as a cornerstone in the region."
Last month, Syria's warring sides and mediators meeting in Kazakhstan failed to agree on the formation of a constitutional committee which is key to ending the seven-year civil war. De Mistura at the time called it a "missed opportunity."
At issue is the 50-member delegation comprising Syrian experts, civil society, independents, tribal leaders and women that de Mistura was authorized to put together by countries attending a Russian-hosted Syrian peace conference in the Black Sea resort of Sochi on Jan. 30.
Agreement has already been reached on a 50-member government delegation and a delegation equal in size from the opposition for the drafting committee. Syrian President Bashar Assad has said his government will only consider amendments to the current constitution, in defiance of the Sochi agreement to have the government, opposition and independents draft a new document.
"We are still working (nights) in order to make sure that if we can there will be an announcement of something regarding the constitutional committee," said de Mistura, whose term ends at the end of the year. "If not, we will have to draw ourselves some conclusions."
The U.N. envoy said that he will likely be delivering his last statement to the U.N. Security Council on Dec. 20 and assess "where we are on the constitutional committee." In the capital Damascus, the Syrian army command said it will demobilize thousands of conscripts and reservists who have been serving in the military for five years by Jan. 1.
The army said in a statement carried by state news agency SANA that the implementation of the order will begin on Dec. 16. The announcement comes after government forces captured wide parts of the country earlier this year including suburbs of the capital Damascus known as eastern Ghouta and southern regions in the county. Demobilizations began after eastern Ghouta was captured in April.
Earlier Monday, U.S.-backed Syrian fighters pushed deeper into the Islamic State group's last remaining stronghold in Syria, capturing an abandoned hospital. The Kurdish-led Syrian Democratic Forces entered the eastern town of Hajin last week and intense fighting has been ongoing since then.
SDF spokesman Mustafa Bali said the U.S.-allied fighters took full control of town's hospital early Monday. Omar Abu Layla, of the activist-run DeirEzzor 24 monitoring group, confirmed the hospital on the edge of town was retaken by the SDF.
Rami Abdurrahman, who heads the Britain-based Syrian Observatory for Human Rights, said the hospital had been destroyed earlier by airstrikes from the U.S.-led coalition. The hospital was close to the front lines and was not believed to be operating when it was hit. The U.S.-led coalition, in a statement, said IS forces had used the Hajin hospital as a platform to engage allied forces on the ground, causing the hospital to lose its protected status.
SDF fighters launched an offensive to capture Hajin and nearby villages on Sept. 10. They have made little progress since then, but last week intensified their attacks under the cover of airstrikes by the U.S.-led coalition.
The Observatory meanwhile released an updated death toll for Syria's conflict, saying that about 560,000 people have been killed since it began in March 2011. The group said it has documented the names of 367,965 of the deceased.
The group said the dead include 111,330 civilians, 65,048 troops and 50,296 pro-government Syrian gunmen. It said the dead also include 65,108 insurgents and 2,619 army defectors. The seven-year conflict has also wounded more than a million people and displaced half of Syria's 23 million-strong population, including 5.6 million who are refugees, mostly in Turkey, Jordan and Lebanon.
Mroue reported from Beirut.