U.N.-brokered peace talks with the Syrian government and opposition began in Vienna yesterday, days before Syria's close ally Russia was due to host separate negotiations to end the war.

Previous rounds of U.N.-sponsored peace talks have made little progress while Syria's Bashar Assad regime forces backed by Russia and Iran have continued to gain ground for years, recovering swathes of the country from opposition fighters. Assad forces recently escalated offensives against two remaining rebel pockets, Idlib in the northwest and Eastern Ghouta near Damascus. Few expect a breakthrough at these two-days talks aimed at addressing issues related to a new constitution, but their host, U.N. Special Envoy for Syria Staffan de Mistura, has continued to express optimism, adding Wednesday: "It's a very critical moment. Very, very critical."

Russia, Turkey and Iran convened eight Syria meetings in Astana last year, with the stated aim of agreeing "de-escalation" zones to ease hostilities in western Syria where the three states wield influence. The Sochi peace congress was announced after their last meeting in December. De Mistura has acknowledged the Sochi congress but it remains unclear how he plans to address it. Western and some Arab states believe that Moscow's initiative would lay the groundwork for a solution more favorable to the regime in Damascus and its allies. The opposition will decide in the next two days whether to attend Sochi, its chief negotiator Nasr Hariri, said Wednesday. He added that the talks would be a test of all sides' commitment to a political solution rather than a military one. Previous rounds have taken place sporadically in Geneva, with a mandate to discuss new elections, reformed governance, a new constitution and the fight against terrorism. But De Mistura has not managed to coax the warring sides into speaking face-to-face, and it was only at the eighth round in December that the rebel opposition united in one delegation, raising modest hopes for direct talks. Despite that, the Syrian regime delegation objected to the opposition's tough line on the future of Assad, and those talks achieved nothing.