Guterres “is confident that the congress in Sochi will be an important contribution” to reviving the peace talks held under UN auspices in Geneva, a UN spokesman said in a statement.
Russia had long sought UN participation in the conference opening Monday in the Black Sea resort of Sochi to lend credibility to its diplomatic efforts to end the six-year war.
Hours earlier, UN envoy Staffan de Mistura ended a ninth round of UN-sponsored talks in Vienna, with no sign of progress toward a peace deal.
“I share the immense frustration of millions of Syrians inside and outside the country at the lack of a political settlement to date,” De Mistura said.
UN spokesman Stephane Dujarric indicated that Guterres had received assurances that the Sochi conference would not seek to sideline the UN talks.
Guterres was briefed by De Mistura on the outcome of the Vienna talks, and has taken into account a statement from Russia that the result of the Sochi conference “would be brought to Geneva as a contribution to the intra-Syrian talks process under the auspices of the United Nations,” the spokesman said in a statement.
The UN chief has “decided to accept the invitation of the Russian Federation to send a representative to attend the Sochi Congress” and has asked De Mistura to go, he added.
Russia has invited more than 1,500 delegates to the two-day conference that the West views with suspicion.
In Vienna, the Syrian Negotiations Commission (SNC) announced it would not be attending the Sochi conference.
– Assad’s fate –
The main opposition coalition fears that Russia will push a peace deal that will keep President Bashar al-Assad’s authority intact after six years of bloodshed.
The Russian foreign ministry welcomed Guterres’ decision, and said the Vienna talks had “focused in particular on the problems of constitutional reform” – a process that could determine whether or how Assad remains in power.
“On these issues, a mutual agreement was reached between the Russian side and the UN representatives, on the sidelines of the Vienna meeting,” said a foreign ministry statement issued in Moscow.
On the ground, Syrian forces have pressed on with an offensive in rebel-held Idlib launched in late December, with Russian backing.
Assad’s forces were on the defensive in the first few years of the war, but since Russia militarily intervened in 2015 they have regained the upper hand.
The United States, Saudi Arabia, Jordan, Britain and France have put forward a proposal that would involve strengthening the role of Syria’s prime minister — at the expense of Assad’s authority, according to a leaked document circulated online.
Syrian government negotiator Bashar al-Jaafari told reporters in Vienna it was “tantamount to a black comedy” that these countries were seeking to shape Syria’s political future.
“All of them have participated in the bloodshed of the Syrian people,” he said of the five nations, blasting the United States as the country “that created ISIS,” and adding that Saudi Arabia was anything but a “beacon of freedom in the east.”
Two weeks ago, Turkey launched air strikes and shelling against Kurdish militias in northern Syria, marking a dangerous new escalation in the conflict.
That development has raised tensions between Turkey – which along with Iran backs the Russian conference in Sochi – and the United States, which has supported the Kurdish militias in the campaign against the Islamic State (IS) group.
More than 340,000 people have died in the war, millions have fled their homes and the fighting has left the country in ruins.