A Russian Tu-22M3 bomber at the Kubinka air base outside Moscow on Saturday. The Russian military has used the long-range bombers during its air campaign in Syria. (Vladimir Isachenkov/AP)

In an unusual announcement Wednesday, Russia said it would halt air raids against Syria’s al-Qaeda affiliate, Jabhat al-Nusra, to give other rebel factions a chance to distance themselves from the extremist group.

The move comes less than a week after Moscow proposed conducting joint airstrikes in Syria with a U.S.-led coalition that is attacking the Islamic State militant group there. U.S. officials have rejected that idea, even as coordination with Russia over a partial truce in the country apparently has increased.

Russian news agencies carried a vague statement attributed to Maj. Gen. Igor Konashenkov, a Russian Defense Ministry spokesman, declaring that unidentified Syrian opposition groups had asked Moscow to suspend attacks.

It said the rebel factions, including in Damascus and Aleppo, agreed to stop “provocative” shelling of government targets. In return, the statement said, Russia would suspend airstrikes for an unspecified period to allow the groups to “separate” from Jabhat al-Nusra.

Jabhat al-Nusra is not party to the truce, but rebel forces that are, including U.S.-backed groups, have coordinated with it during attacks on government positions.

Rebel fighters contacted by telephone, however, denied any communication with Russia, which began a campaign of airstrikes last fall on behalf of Syrian President Bashar al-Assad. Russian warplanes have dealt crippling blows to opposition forces.

Since taking hold in February, the cease-fire brokered by Russia and the United States has all but collapsed, with many Assad opponents blaming continued assaults by pro-government forces.

“The Russian statement is totally inaccurate,” said Qutaiba al-Dughaim, a fighter with the Northern Division rebel group. “None of the rebels in northern Syria have any contact with the Russians.”

He said the Russian announcement was an attempt to further divide Syria’s fractured opposition.

Rebel fighters have been alarmed by signs of growing U.S. coordination with Russia even though Washington and Moscow disagree on Assad’s fate. U.S. officials say the interaction involves video conferences limited to flight safety. Currently, both countries target the Islamic State independently.

Rebel groups say the United States is more interested in fighting the extremist group than backing them against Assad’s forces. They fear that the United States will bend to Russian demands, leaving Assad in power in the hope of joint operations against the Islamic State.

Mark Toner, a State Department spokesman, on Monday dismissed the possibility of military cooperation with Russia. U.S. officials have been discussing with Moscow “proposals for sustainable mechanisms to better monitor and enforce” the cease-fire, he said. “We’re not looking at joint operations.”

The Russian announcement Wednesday could be related to the issue of labeling terrorist groups, a major point of contention in holding the truce together. Despite Russian requests, the United States has rejected applying the terrorist designation to Ahrar al-Sham, an anti-Assad Islamist group allied with Jabhat al-Nusra.

Syrian state media blamed Ahrar al-Sham for suicide bombings in pro-government coastal areas Monday that killed more than 100 people. Ahrar al-Sham denied responsibility for the attacks, which were later claimed by the Islamic State.

Zakaria Zakaria in Istanbul contributed to this report.