Staffan de Mistura announced the date after reporting to the Security Council on the results of the last round of talks on ending Syria's six-year war.

"My current intention is to bring the invitees back to Geneva for a fifth round, with a target date of the 23rd of March," he told reporters after the meeting.

The new round will focus on governance, constitutional process, elections and counter-terrorism and there may also be discussions on reconstruction, said De Mistura.

The European Union and the United Nations will host a conference in Brussels on April 5 on Syrian reconstruction but the assistance will only start flowing once a political transition is in place.

US Ambassador Nikki Haley told reporters after the meeting that the new US administration supports the Syrian peace process and wants the talks in Geneva to continue.

"This is very much about a political solution now at this point and that basically means Syria can no longer be a safe haven for terrorists," she said.

"We've got to make sure that we get Iran and their proxies out," she added.

Russia and Iran are backing President Bashar al-Assad militarily in the war against a myriad of opposition fighters backed by Turkey, the United States and Gulf countries.

"We are going to continue to watch the process, but it's one that we support and one that we want to see a solution to," she said.

Russia, Turkey and Iran are expected to convene a new meeting in the Kazakh capital of Astana to prepare for the Geneva talks.

Previous rounds of peace talks have hit a wall over the future role of Assad, accused by the West of stoking the violence that has left 310,000 dead since March 2011.

The UN envoy sounded cautiously optimistic, saying that while there were no "miracles" during the last round, "we achieved much more than many people had imagined we could have."

"No one left. Everybody stayed. They were focused. We got an agenda. We got a timeline and we got some agreement, even on substance," he said.