The Syrian Observatory for Human Rights had earlier said that a rebel group Failaq al Sham is withdrawing its forces and heavy arms from the demilitarised zone in Syria's Idlib.
Syrian rebels denied on Sunday they had pulled any heavy arms from a major opposition bastion in the north, as the deadline to implement a demilitarisation deal there draws closer.
Russia and Turkey agreed earlier this month to create a demilitarised zone around the opposition stronghold of Idlib.
The deal has so far averted a massive assault on the region by Syrian regime, but its implementation in areas packed with rival groups is expected to be complex.
The National Liberation Front, a pro-Turkey rebel alliance, welcomed the agreement but said on Sunday it had not yet moved any heavy arms from the planned zone.
“There have been no withdrawals of heavy weapons from any area or any front. This report is denied, completely denied,” NLF spokesman Naji Mustafa told AFP.
The Syrian Observatory for Human Rights monitor had earlier said one faction of the NLF - Failaq al Sham - began withdrawing its heavy weapons under the Turkish-Russian agreement.
Failaq al Sham is the third largest group among the rebel groups in Northwest Syria, according to the monitor.
A spokesman for the group also told AFP on Sunday it had not moved any forces or arms.
“There have been no changes in the location of weapons or redistribution of fighters, even as we remain committed to the agreement reached in (the Russian resort of) Sochi,” said Sayf al-Raad.
“We are still coordinating with the Turkish guarantor on following the agreement and ways to implement it,” he added.
UN diplomats say a recent agreement between Russia and Turkey to set up a buffer zone in the last major rebel stronghold of Idlib has created an opportunity to press ahead with political talks.
The Russian-Turkish deal averted a large-scale assault by Russian-backed Syrian forces on the province, where three million people live.
Dominant group yet to respond
Under the accord reached on September 17, rebel and opposition factions would withdraw their heavy weaponry from the buffer zone.
Some rebels have cautiously accepted the deal, but others rejected it, saying the zone to be set up by October 15 would only encompass territory currently under rebel control.
The dominant force in the region bordering Turkey, the Hayat Tahrir al Sham (or HTS) alliance led by fighters of Syria's former al Qaeda affiliate, had on Saturday still not responded to the deal.
The demilitarised zone will be 15 to 20 km (10 to 12 miles) deep, run along the contact line between rebel and regime fighters, and will be patrolled by Turkish and Russian forces.
The Syrian conflict, now in its eighth year, has killed hundred of thousands, mostly civilians, and has generated around 5.6 million refugees in the Middle East.