Geir Pedersen arrived on a two-day visit to Damascus on Saturday, in his third official visit to the country since assuming his post in January.
He met Sunday morning with Syrian Foreign Minister Walid al-Muallem.
“We have had very detailed substantial discussions,” Pedersen told reporters after the meeting.
“We are now addressing all the issues so all the issues are at the table,” AFP quoted him as saying.
State news agency SANA said Pedersen and Muallem discussed ongoing efforts to advance the political process, including moves to form a committee tasked with drawing up a post-war constitution.
Pedersen first visited Damascus in January then on March 17, when he discussed with Muallem the political solution to the ongoing eight-year conflict.
He became the fourth UN negotiator aiming to resolve the war following the resignation of his predecessor Staffan De Mistura.
Since early January, he has traveled extensively to meet with the regime, opposition and others.
The veteran diplomat faces a difficult task of reviving negotiations between the regime and the opposition at the UN after his predecessor failed to reach a solution due to conflicting demands from both sides of the conflict.
De Mistura’s efforts focused on the formation of the constitutional committee proposed by the three guarantors of the peace process in Astana, which are Damascus’s allies Russia and Iran and opposition supporter, Turkey.
The opposition is demanding a new constitution for the country, while the regime wants to discuss the existing constitution and amend some of its articles.