A Syrian opposition group that is close to Russia and tolerated by Damascus will meet UN envoy Staffan de Mistura at peace talks in Geneva, a delegation member told AFP Wednesday.

"We received an invitation to take part in the Geneva talks," said Fateh Jamous, a member of the so-called Moscow Group, which includes ex-Syrian deputy prime minister Qadri Jamil who is considered a moderate opposition leader by the regime.

Jamil, who was sacked by Syrian President Bashar al-Assad in 2013, was in Geneva for an earlier round of talks that collapsed in February but did not meet with de Mistura at the time.

"Our invitation is proof that the talks have entered a new, more serious stage," Jamous said.

The Saudi-based High Negotiations Committee (HNC), more hardline than the pro-Russia group, has insisted that it be considered the only representative of Syria's opposition at the talks.

HNC spokesman Salem al-Meslet told AFP on Tuesday that expanding the number of opposition delegations was "unacceptable".

Assad's fate is seen as the main obstacle to any deal in Geneva, with the HNC insisting that the Syrian leader must go before any transitional government is agreed.

- 'Consensus' needed -

Jamous charged the HNC with imposing "conditions that we consider contradictory to the principle of consensus, including the condition of the president's departure."

"We will present to de Mistura our vision of the transitional period, which cannot happen without consensus from all sides," he added.

De Mistura said Tuesday that regime ally Russia's surprise decision to begin withdrawing its forces from Syria could be "positive" for efforts to find a political solution to the brutal five-year war.

It "is not a coincidence, or at least we should not consider it a coincidence, that the (pullout) decision took place at the very beginning" of the talks, the UN envoy said following his Tuesday meeting with the HNC.

Experts and Western leaders have said the Russian withdrawal could be part of a broader effort from Moscow to pressure its long-time ally Assad into negotiating an end to the conflict that has killed more than 270,000 people and displaced millions.

De Mistura on Wednesday met with the regime delegation led by Syria's UN ambassador Bashar al-Jafaari.

The UN envoy has said that both the HNC and Damascus had submitted their views on how to move forward, and he would try to "analyse" their positions to find any possible common ground.

There was no immediate indication as to the possible impact of the pro-Russia's group's inclusion in the process.

But wrangling over delegates has hampered past negotiations, especially the contentious issue of including Syrian Kurdish groups, who have not been invited to Geneva despite a push from Russia.

The talks are aimed at striking a deal that will create a transitional government, a new constitution and general elections within 18 months.

De Mistura has acknowledged that huge gaps exist between the various sides but voiced hope that new facts on the ground, including the Russian withdrawal, could spark "momentum" towards a breakthrough.

US Secretary of State John Kerry said Tuesday he would meet with Russian President Vladimir Putin to "try to take advantage of this moment," which he described as the best opportunity in years to end the bloodshed in Syria.

He is expected to go to Moscow some time next week after a trip to Cuba.

The current round of talks in Geneva is expected to end on March 24, with a new round possibly beginning in early to mid-April.