After peaceful demonstrations were met with violence in 2011, protesters took up arms against Syrian government forces. A brutal civil war followed with hundreds of thousands dead and millions displaced. A fragile cease-fire has quieted some of the fighting, for now. (Liz Sly,Jason Aldag/The Washington Post)

Peace talks described as a last-chance effort to avert even greater bloodshed in Syria resumed Monday, a day before the fifth anniversary of the country’s peaceful uprising that eventually devolved into catastrophic civil war.

Although still bitterly divided, the warring parties agreed to gather here in Geneva again for U.N.-sponsored talks to hammer out differences. A similar round of negotiations collapsed just over a month ago because of a pro-government offensive backed by Russian air raids near the northern Syrian city of Aleppo.

Now the stakes couldn’t be higher, warned Staffan de Mistura, the U.N. Syria envoy tasked with ending a war that has killed a quarter-million people, produced an extraordinary refugee crisis and fed the rise of Islamist extremists. He told journalists at the U.N. headquarters in Geneva, where the talks are being held, that “the only plan B available is the return to war, and to an even worse war than we had so far.”

He plans to shuttle between the government and opposition delegations in so-called proximity — or indirect — talks.

De Mistura briefly met with the Syrian government delegation, led by Bashar al-Jaafari, and is to hold a similar meeting Tuesday with the opposition. “It was a useful meeting and I think we clarified quite a lot of issues,” de Mistura said afterward, although he provided few details.

Following the meeting with the U.N. envoy, Jaafari, flanked by advisers and government officials, described the new talks to journalists as “positive and constructive.” His delegation will again meet with de Mistura on Wednesday.

Already, however, Syrian officials have dismissed calls by the opposition for the formation of a transitional government with full executive authority. Such an authority would exclude President Bashar al-Assad, a non-starter for the government and a major sticking point in finding a resolution to the conflict.

Even though Assad’s future still poses perhaps the most formidable obstacle in brokering peace, opposition figures see signs of hope. Some of them cite as possible progress a partial truce negotiated by the United States and Russia that has managed to hold for more than two weeks despite violations by pro-government forces, including alleged land-grab attempts and airstrikes on civilian populations.

“The only thing we can do now is continue with this cessation of hostilities,” said Hind Kabawat, a member of High Negotiations Committee, an umbrella group representing the opposition at the talks. “Fatigue has set in on both sides, and there is a strong sense that the only solution to this conflict is a political solution.”

She called for Russia to use its influence to restrain Syria’s government, which Moscow has backed with punishing airstrikes against rebel groups since September. “Russia is in control of the Syrian regime, and we need Russia to force the regime to abide by the cessation of hostilities.”

The military balance has shifted in Assad’s favor after Russia’s intervention, chipping away at rebel control over key areas of northwestern Syria and near the capital, Damascus. The Syrian leader now has Moscow and thousands of Shiite Muslim militiamen from Iran, Lebanon and Iraq providing much-needed manpower to his beleaguered armed forces.

Five years ago, few would have ever expected that their uprising against the Syrian leader — a peaceful Arab Spring revolt — would turn into a violent proxy war for regional actors.

On March 15, 2011, Syrians took to the streets in Damascus for unarmed rallies that would spread like wildfire across the country and eventually be met with utter brutality by Assad’s security apparatus. Nor would most Syrians back then have expected that the Islamic State and al-Qaeda-affiliated Jabhat al-Nusra would hijack their revolt.

On Monday, activists said residents and opposition fighters in the northwestern province of Idlib staged angry rallies to protest attacks a day earlier by Jabhat al-Nusra. The extremist group arrested several rebels affiliated with a Free Syrian Army outfit known as Division 13, killing a number of them and seizing weapons, according to activists and the Britain-based Syrian Observatory for Human Rights monitoring group.

Rebel groups in Idlib face immense pressure, fending off assaults by both al-Qaeda militants and pro-government forces, which appear to be gearing up for assaults on the province.

“We’re seeing regime troops preparing for an assault, and they are supported by Russian airstrikes and Iranian soldiers,” said Ibrahim al-Idlibi, a rebel affiliated with a Free Syrian Army faction.

Despite all this, residents in Idlib also have demonstrated that the core message of Syria’s uprising still rings true for many. On Friday, scores of people in Idlib and other rebel-held areas of the country held non-violent rallies calling for revolution and waving pro-opposition flags in town squares.

“These protests show that the revolution still lives on for the Syrian people,” said Kabawat, the opposition representative.

Zakaria Zakaria in Istanbul contributed reporting