The Syrian army said on Monday it was resuming military operations in a Russian-led campaign in northwest Syria that has uprooted tens of thousands and killed hundreds, blaming Turkey for not abiding by its commitments under a truce deal.

Syrian state media said on Thursday the ceasefire would depend on militants fulfilling a Russian-Turkish deal that tried last year to create an Idlib buffer zone.

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“The agreement to a truce was conditional. This did not happen.. We resume our military operations against terrorist organizations,” said the army statement.

Meanwhile, Syrian militants have shelled the outskirts of the Hmeimim air base in northwest Syria, Russia's Defense Ministry said on Monday. 

The air base was unaffected by the attack, the RIA news agency quoted the ministry as saying. 

Since Damascus declared a ceasefire on Thursday night, its warplanes have not mounted air strikes, though the combatants are still shelling each other.

Damascus accuses Turkey and the rebels it supports of failing to comply with the terms of the de-escalation agreement which require heavy weapons and jihadist insurgents to be withdrawn from a buffer zone.

Under its deals with Moscow, Ankara has forces stationed on the ground in the Idlib region at a dozen military positions.

The Turkish Foreign Ministry declined immediate comment.

The region - including Idlib province and parts of nearby Hama - was part of the last major stronghold of armed opposition to President Bashar Assad, who has vowed to reclaim all of Syria.

Rebel factions have agreed to the latest ceasefire while reserving the right to respond to attacks.

The Russian-led campaign has been costly to Moscow and its Syrian ally. They appear to have failed to secure any significant territorial gains despite weeks of relentless bombing and have suffered heavy human losses, according to Western military experts.

Rebels say Moscow has deployed special troops to make a military breakthrough with no success in one of the biggest campaigns waged by Moscow in Syria since its direct intervention in Syria in September 2015.

For three months, an army offensive backed by Russia has killed at least 400 civilians in northwest Syria and uprooted more than 440,000 people, the United Nations says.

Residents and rescuers say the three-month-old campaign has left dozens of villages and towns in ruins.

Russia and its Syrian army ally deny their jets indiscriminately hit civilian areas with cluster munitions and incendiary weapons, which residents in opposition areas say are meant to paralyze everyday life.

Since Damascus declared a ceasefire on Thursday night, its warplanes have not mounted air strikes, though the combatants are still shelling each other.