BEIRUT — With much of Syria calm for the past 24 hours, a powerful al-Qaida-linked group sharply criticized the U.S.-Russian-brokered cease-fire, saying Tuesday its real aim was to keep President Bashar Assad in power.

The extremist group was in talks with other rebel factions for a possible merger, a move that could dash Washington and Moscow’s hopes of distancing it from the wider insurgency and sabotage the truce.

The denunciation of the deal came as activists and state media said the truce, which took effect at sunset Monday, was holding despite some violations. The Syrian army said it would abide by the cease-fire until midnight Sunday, while maintaining its right to defend itself against any violations.

The truce excludes al-Qaida’s affiliate, known as Jabhat Fatah al-Sham, and the more powerful Islamic State group, which are both designated terrorist organizations by the United Nations. The first week will be crucial: During that time, all fighting between Assad’s forces and the rebels is to stop, although Assad’s forces can continue airstrikes against ISIS and al-Qaida-linked militants.

If the calm holds for seven days, the U.S. and Russian militaries would then set up a new center to coordinate strikes against ISIS and the al-Qaida affiliate, previously known as the Nusra Front.

The Jabhat Fatah al-Sham statement came a day after Syria’s largest insurgent groups expressed misgivings over the deal for excluding the al-Qaida-linked militants, who have been fighting alongside the rebels against Assad’s forces. A truce in February that lasted several weeks also excluded ISIS and al-Qaida-linked groups.

In its statement, the al-Qaida affiliate accused the U.S.-Russian-brokered deal of “conniving” to divide the insurgents and “target them one by one, while distancing Assad’s regime from the battle and preserving” his hold on power.

“The aim of the Russian-American agreement is to defeat Syrian jihad, break its arm and cut its teeth,” the group said.

Mostafa Mohamed, the group’s director of media relations wrote on his Twitter account: “Let it be known. We don’t take orders from hypocritical tyrants. We will continue in this cause, standing in solidarity with our brothers.”

Jabhat Fatah al-Sham has been working to improve its image and distance itself from al-Qaida. In July, its leader, Abu Mohammed al-Golani, publicly showed his face for the first time in a video in which he announced the group’s name change and said it was cutting ties with the international terror organization.

The group has been in talks for weeks to merge with other insurgent groups so that it can market itself as a Syrian faction — a move that would anger the United States, which has urged Syrian rebels to distance themselves from al-Qaida-linked militants.

One of Syria’s most powerful factions, Jabhat Fatah al-Sham’s battlefield alliance with other insurgent groups makes it difficult for the United States to target them without the danger of inflicting harm to other opposition groups.

A Jabhat Fatah al-Sham commander in the northern province of Aleppo told The Associated Press the group could announce its merger with the ultraconservative Ahrar al-Sham group “in the near future.”