The lead government negotiator, Bashar al-Jaafari, speaking to reporters after the opening session, responded by calling the opposition delegation “armed terrorist groups,” and accused them of “impertinent” and “provocative” behavior.
The tension demonstrated the challenges that remain for Russia, the Syrian government’s most powerful backer, as the Russian government tries to show its approach can accomplish more than the largely fruitless efforts led in past years by the United States and the United Nations.
Expectations for progress had been low. Many diplomats and analysts say the more meaningful talks are those that have been held in recent months, largely in secret, among Russia, Turkey and Iran.
The meeting in Astana, meant to send the message that Russia would seek to resolve the conflict in its sphere of influence, was markedly different from the United Nations-sponsored talks that have taken place in recent winters in Geneva.
Delegates crisscrossed the towering atrium of the Rixos Hotel in the remote Kazakh capital built 20 years ago on the orders of Nursultan Nazarbayev, the former Communist boss who has been the country’s president since it became independent with the collapse of the Soviet Union in 1991. He has a reputation as a pragmatic strongman and enjoys good relations with Russia and Turkey.
Palm trees planted indoors belied the subzero temperatures and blowing snow outside, as a flute-and-piano duo wearing evening gowns played “Strangers in the Night” and the theme from “Titanic.” Western diplomats, largely sidelined, huddled in the hotel’s Irish Pub, and the United States ambassador to Kazakhstan, who was invited over Iran’s objections and attended only as an observer, avoided reporters.
When the Americans had participated in previous rounds of talks in Geneva, the meetings took place at the Palace of Nations, one of the stolid lakeside edifices built when the United Nations was formed after World War II. Those buildings symbolized a postwar order that tried to institutionalize human rights and the laws of war, an order associated with American leadership — or domination — amid the tensions of the Cold War.
Now, the role of the United States in Syria and across the Middle East is widely seen as having receded under the former President Barack Obama, and its future remains uncertain. Mr. Obama, while backing some rebel groups, resisted deeper American involvement in the Syrian conflict, ceding the leading role to Russia. His successor, President Trump, has signaled broad approval of Russian leadership and policies and sent mixed messages on Syria.
Officially, all sides in the Syrian conflict describe the goal of the talks in Astana as reaffirming a tenuous cease-fire in order to revive the Geneva talks. The cease-fire, started in December and known formally as a cessation of hostilities, is largely ignored in many parts of the country and excludes jihadist groups, including the Levant Conquest Front and the Islamic State.
A strengthening of the cessation across Syria, the United Nations envoy Staffan de Mistura said Monday, could pave the way for discussion of more substantive political issues at talks scheduled for February in Geneva. The United Nations initially resisted anything more than an observer role in the talks in Astana, but Mr. de Mistura at the last minute agreed to act as a mediator and was shuttling between the delegations who were in separate rooms.
Western diplomats were also watching warily to see whether the talks in Astana could be a Russian effort to ultimately replace the Geneva discussions, which the Russian government has criticized. The Syrian government and the Russians have long argued that the Geneva framework, calling for a transitional body with full governing powers, does not require President Bashar al-Assad to step down, while the opposition has insisted that it does.
But as a practical matter, an increasing number of Western countries, including the United States, and even some of the rebels’ backers in the Middle East, like Turkey, have moved toward the Russian position.
With Turkey mainly concerned about checking Kurdish militants within its borders and in Syria, and the United States focused on battling Islamic State militants, they have stopped pushing loudly for Mr. Assad to step down ahead of a settlement, instead signaling that they could accept some role for him in a transitional political arrangement.
There were signs on Monday of Russian willingness to apply pressure on the Syrian government to keep the talks on track. The tense exchanges in Astana were followed by a Russian statement unusually critical of the Syrian government: The state-owned news agency RIA Novosti said monitors of a cease-fire in Syria were “particularly concerned about sporadic violations of truce by the Syrian government forces” — echoing a complaint of rebels.
Russia’s large-scale air campaign, which began in the fall of 2015, helped forces loyal to Mr. Assad drive rebels from their foothold late last year in half of the important city of Aleppo, an offensive criticized by the opposition for indiscriminate air and artillery attacks on civilians. Some rebel groups also shelled civilians in government-held areas.
Now one of the main battles is over Wadi Barada, a besieged rebel-held area in the watershed that provides most of the drinking water for Damascus, the Syrian capital. Water supplies have been cut off for weeks, with the government blaming rebels and rebels blaming the government.
Mr. Jaafari, the chief Syrian government negotiator and his country’s envoy to the United Nations, was incensed that Mr. Alloush, the rebel representative, had sounded the alarm over the plight of people in Wadi Barada. He said raising concerns about government attacks on Wadi Barada was tantamount to defending the Nusra Front, the former name of the Levant Conquest Front, which is excluded from the cease-fire. Residents and rebel fighters in Wadi Barada say that some Nusra fighters are present, but they are a minority among other rebel groups and civilians.
Mr. Jaafari said that rebel groups had “misunderstood” the terms of the cease-fire, adding, “We had guarantees from their guarantors that they would behave, but they did not behave.”
Fares Bayoush, a negotiator from an American-backed rebel group who defected from the Syrian Army, said, “He is the one who misunderstood.”
Because of an editing error, an earlier version of this article misstated the given name of the United Nations envoy for Syria. He is Staffan de Mistura, not Stefan.