The Syrian Observatory for Human Rights, a war monitor, reported cautious calm in the enclave on Friday amid a halt to airstrikes by the government and Russian jets.
The calm was shattered by intermittent shelling exchanged by the government forces and jihadist groups in the area, the Britain-based watchdog added.
An Idlib resident told dpa that the government shelling had targeted some rebel areas Friday morning, but it has been quiet since noon.
The al-Qaeda-linked Hayat Tahrir al-Sham, a rebel group that mainly controls the province of Idlib, called in a statement on its fighters to to take "extra precautions because the regime and their allies are known for treachery."
Syria's state news agency SANA meanwhile reported that the rebels had breached the truce by allegedly firing five rockets on the coastal province of Latakia, a stronghold of Syrian President Bashar al-Assad.
The agency added that the shelling on rural Latakia had killed one civilian and injured three others.
In April, government forces started a wide-scale offensive against rebels in Hama and Idlib that has since displaced some 400,000, according to UN estimates.
At least 800 civilians have been killed there since the onslaught started, according to the Observatory.
On Thursday, SANA, citing a military source, said the truce would take place on the condition that a Turkish-Russian deal that was reached in September to create a demilitarized buffer zone in Idlib is implemented.
The September agreement provides for the creation of a 15-to-20-kilometre-wide buffer zone to separate government troops and rebels in Idlib and adjacent areas.
The Russian-Turkish deal has since been repeatedly violated amid an exchange of blame between the Syrian government and the opposition.
The truce announcement was made as a new round of talks on Syria's peace was held in the capital of Kazakhstan, Nur-Sultan.
The meeting was attended by delegates from Iran, Russia and Turkey, the Syrian government and the opposition
According to SANA, the guaranteeing countries of the talks - Russia, Iran and Turkey - affirmed in a final statement their adherence to Syria's territorial integrity and sovereignty.
Participants in the Nur-Sulatn talks also stressed the need for establishing calm in the de-escalation zone in Idlib, SANA reported.
Representatives from Syria's neighbours - Jordan, Lebanon and Iraq - participated in the talks for the first time.
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