The UN embarked on fresh efforts Thursday (January 25th) to jump-start Syrian peace talks that Western countries and the opposition fear are being undermined by a separate Russian diplomatic push, AFP reported.

The two days of talks in Vienna come after eight previous rounds in Geneva, during which the two sides failed to even meet each other.

The previous attempts stumbled in particular over the fate of Syrian President Bashar al-Assad, with the government delegation refusing to meet the opposition face-to-face until they drop demands that he leaves office.

The Syrian government's top negotiator Bashar al-Jaafari made no comment as he arrived at the UN in Vienna to meet the world body's special envoy Staffan de Mistura.

The main opposition group, the Syrian Negotiations Commission (SNC), said it would sit down for separate talks with the envoy at 4:00 p.m.

De Mistura said on Wednesday that the negotiations came at a "very, very critical moment".

Nasr al-Hariri from the SNC said the discussions would be "a real test for all the sides".

French Foreign Minister Jean-Yves Le Drian said meanwhile in Paris that the talks were the "last hope" for reaching a political solution to a seven-year conflict that has claimed more than 340,000 lives.

The Vienna talks come ahead of a separate peace conference next Tuesday in the Russian Black Sea resort of Sochi, backed by Russia, Iran and Turkey.

The focus in Sochi will be on hammering out a new constitution, according to the opposition, something that de Mistura also wants discussed in Vienna.

While Assad's government has said it will go to Sochi, the SNC has not yet decided, even after a recent visit to Moscow.