BEIRUT — Syria’s government has agreed to attend a U.S.-Russian-brokered peace conference, according to Moscow. While this development might seem at first glance to be a step toward ending the civil war, strong skepticism persists on both sides.

Doubting that Damascus is serious and may be stalling while government forces make battlefield gains, the Syrian opposition has demanded guarantees that President Bashar Assad’s departure top the agenda; Russia questioned whether the fragmented opposition is capable of negotiating with one voice.

The war has killed more than 70,000 people, and both sides are firmly entrenched in their positions and appear unwilling to compromise to stop the carnage and chaos engulfing the country.

“We are not willing to enter a tunnel with no guarantees of a light at the end of that tunnel,” said Muhieddine Lathkani, a London-based Syrian opposition figure. “There’s still a lot of fogginess surrounding the talks and we are waiting for some answers.”

Much about the conference remains up in the air, including the date, the agenda, the timetable and the participants. Officials have said it should be held in June.

The U.S. is working to convince Syrian rebels to attend, and the Russians have been pressing Assad’s regime to take part as well.

U.S. officials said Secretary of State John Kerry will extend a seven-day trip through the Middle East and Africa by one day to meet with Russian Foreign Minister Sergey Lavrov on Monday to discuss their joint initiative.

The opposition is deeply suspicious about Assad’s intention to hold serious peace talks, and the fact that the announcement was made by the Russians — Assad’s government has not issued a definitive statement of its own — added to the skepticism.

“We would like to hear from the spokesman of the Syrian government. Why is Russia speaking on behalf of Syria?” opposition figure Louay Safi said.

Assad has indicated that he will stay in power at least until the 2014 presidential election in Syria, and that has nothing to lose by agreeing to take part in the conference, or at least going through the motions.

While going along with an initiative proposed by his Russian allies and agreeing to participate, Assad gains more time to continue with his crackdown on the rebels.

The regime has been emboldened by recent successes in the war, including advances in the strategic town of Qusair near the border with Lebanon.

Kerry made clear at a “Friends of Syria” conference in Jordan this week that more aid to the rebels would be coming if the regime refuses to cooperate with an international effort to form a transitional government. The U.S. is still reluctant to join those providing the rebels with lethal military aid, but some in the opposition are hoping that will change.

European Union foreign ministers plan a meeting Monday in Brussels to decide on whether to allow members to ship arms to the rebels.

Christopher Phillips, a lecturer in International Relations of the Middle East at Queen Mary, University of London, said both sides believe that engaging in diplomacy is the price for weapons.

“The voices of power on both sides believe they can win the conflict militarily,” he said. “With that as a starting point, it’s difficult to see to see how a peace conference is going to achieve the goals it wants.”