UN Syria envoy Staffan de Mistura will hold talks Tuesday with top US and Russian officials in Geneva in a bid to revive flagging peace talks, his office said.

US mission spokesman Paul Patin told AFP that the State Department's special envoy for Syria Michael Ratney will be at the meeting, while Russia's Ria-Novosti news agency said Moscow will be represented by deputy foreign minister Gennady Gatilov.

De Mistura's spokeswoman Jessy Chahine, who confirmed the meeting, gave no details about its agenda, but the UN envoy has been trying to save a peace process which some feared was facing total collapse.

US Secretary of State John Kerry and Russian counterpart Sergei Lavrov earlier this month announced an agreement on "concrete steps" to salvage a failing ceasefire in Syria, a key step before negotiations can resume.

Kerry and Lavrov were also due to meet on the sidelines of an Asian summit in Vientiane, Laos on Tuesday.

When peace talks to end the five-year war restarted in February, de Mistura voiced hope that he could strike a deal for a new transitional government in Syria by August 1.

While that deadline will certainly not be met, the UN envoy has repeatedly stressed that there is no "Plan B" for Syria aside from the peace process, urging President Bashar al-Assad's government and opposition leaders to stick with the negotiations.