BEIRUT — A leading Syrian opposition group called on the United Nations to retake charge of the peace process for war-torn Syria, on Thursday, after Russia announced it would host parallel talks later this month.

The High Negotiations Committee said Russia was undermining the U.N. and imposing its own rules for Syria, where over 400,000 people have been killed in a six-year-long civil war.

Russia is a steadfast ally of Syrian President Bashar Assad. Moscow has sent air support and military advisers to fight alongside Syrian government troops against armed rebels and other opponents. Moscow says it’s fighting a war on terrorism.

The HNC said in a statement it would “not participate in any events held outside the umbrella of the United Nations,” and accused Moscow of “rehabilitating” the Syrian government.

The Syrian National Coalition, a Turkey-based opposition group which forms the political umbrella for armed rebels loosely known as the Free Syrian Army, also said they would stay away from the proposed meeting in Sochi.

The U.N. has not said whether it will attend talks in Sochi on Nov. 18, just 10 days before the international body convenes its own talks between the government and opposition in Geneva.

The Sochi talks will open a fourth track of talks between parties to the deeply intricate conflict in Syria. The U.N.’s own program out of Geneva has been supplemented by “technical” talks in the Kazakhstan capital of Astana, brokered by Iran, Turkey and Russia, the chief international parties to the war in Syria.

And Russia periodically opens a third track through Cairo. Egypt has provided a base to Syrian reformists seen as acceptable to the Damascus government.

But with the balance of power in Syria firmly in Assad’s favor — thanks in large part to Russia’s overwhelming military intervention — talks have produced few tangible results, leading the rebels to accuse Russia and Damascus of stalling as they pursue results on the ground.

The Western-backed HNC and various rebel groups have demanded any process stay in line with the legally binding U.N. Security Council resolution 2254, which mandates a locally led “political transition” for Syria. Other factions, led by the al-Qaida-linked Hay’at Tahrar al-Sham — Arabic for Levant Liberation Committee — have refused negotiations with Damascus.

Assad’s government has refused to put its own future up for negotiations.

Meanwhile, Syrian opposition activists said at least six people have been killed in government shelling of a rebel-held town outside the capital Damascus.

The Ghouta Media Center and the Syrian Observatory for Human Rights reported the deaths Thursday in the town of Douma. The town is part of the eastern suburb of Damascus known as Eastern Ghouta.

Residents of the area have been living under a suffocating government blockade amid intense bombings. The violence and siege have continued even though the suburbs are part of a de-escalation agreement guaranteed by Syrian government backers Russia and Iran.