The UN's Syria envoy will meet ambassadors from the five permanent members of the United Nations Security Council on Wednesday in Geneva, ahead of planned talks to end the country's civil war, a statement said.

Envoy Staffan de Mistura has been trying to secure support for a fresh round of negotiations, which are provisionally scheduled to start on January 25, and are aimed at resolving the brutal conflict.

His meeting with Britain, China, France, Russia and the United States will be "at the ambassadorial level," and will take place at the UN's European headquarters in Geneva, UN spokesman Ahmad Fawzi said.

No details were given as to the agenda of the talks.

Speaking to journalists earlier on Tuesday, Fawzi said De Mistura was going to spend this week trying to "nail down... the timing and the framework" for the talks.

Last week, Damascus pledged to take part in the negotiations, but key opposition groups have withheld such commitments.

The Security Council has endorsed an ambitious 18-month plan to end Syria's nearly five-year war which has killed more than 260,000 people and forced more than 4 million others to flee the country, with a negotiated political solution seen as essential to ending the violence.