Three soldiers were killed on Tuesday when suicide bombers disguised as farmers hit a military post in Hama, western Syria, which is part of a de-escalation zone overseen by Russia and Turkey.
The attack will put pressure on the agreement between Russia and Turkey, who are the self-appointed guarantors of the observance of a ceasefire in the Idlib Governorate.
Home to some three million people, a major assault by the regime could risk hundreds of thousands of lives, with the UN having warned of a humanitarian catastrophe.
The incident follows a number of attacks by the Syrian Army in the area in recent days.
According to a report by Syria's state media, a group wearing traditional farmers' clothes and explosive belts approached a regime outpost in the countryside north of Hama at around 3am local time on Tuesday morning.
When the soldiers on watch opened fire, the terrorists fired back with machine guns, mortars and then detonated their explosives.
Three of the soldiers and all of the attackers were killed, and a tank was "destroyed", it was reported.
No one immediately claimed responsibility for the attack, but monitor the Syrian Observatory for Human Rights said that it had been carried out by Ansar Al Tawhid, an insurgent group affiliated with Al Qaeda. They also reported that six soldiers had died in the incident.
The demilitarised zone around Idlib and Hama was created after Russia and Turkey struck an agreement last September to oversee the area and help reduce fighting to prevent a Syrian regime offensive.
The situation has recently deteriorated despite the increased presence of both country's troops.
There have been attempts to quell the violence, but tit-for-tat attacks between the regime's forces and rebels continue in an area that was once an opposition stronghold.
Turkey's President Recep Tayyip Erdogan visited Moscow on Monday to meet Russian President Vladamir Putin for the third time this year to discus, among other things, their continued co-operation in Syria.
Mr Erdogan said prior to the meeting that his army is ready to launch an offensive against Kurdish groups in northern Syria.
"Our preparations on the border are finished, everything is ready for an operation,” Mr Erdogan told reporters. “We can begin it at any moment.”
