Turkey and Russia have completed their first joint military patrol along a strategic highway in Syria's northwestern region, the Turkish defence ministry said.

"Within the framework of the Moscow agreement, the 1st joint Turkish-Russian land patrol on the M4 highway has been completed with the contribution of air and land assets," the ministry said in a statement on Sunday.

Earlier, Russian news agencies reported that Moscow had sent military police and armoured vehicles to the patrol, which began from the settlement of Tronba in Idlib province, the last opposition-held stronghold in the country.

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The patrols are part of a ceasefire deal reached earlier this month by Turkey, which backs certain opposition groups, and Syrian government ally Russia to halt an escalation of violence in Idlib that has displaced nearly a million people and brought the two countries close to direct confrontation.

Turkish President Recep Tayyip Erdogan said earlier this month that his country would not shy away from even stronger military action in Idlib if the ceasefire is broken.

Under the ceasefire deal, Turkey and Russia are meant to also establish a security corridor either side of the key M4 highway, which links Syria's east and west.

The corridor stretches 6km (3.7 miles) to the north and 6km to the south of the M4 - effectively advancing Russia's presence further north into Idlib.

The two countries are likely to face obstacles during their joint patrols, Al Jazeera's Sinem Koseoglu, reporting from Istanbul, said.

"Since yesterday, we have seen opposition activist groups holding sit-ins and demonstrations on the M4 highway to protest against the Russian presence in Idlib," she said.

Hay'et Tahrir al-Sham (HTS) - an armed group previously linked to al-Qaeda that is not backed by Turkey - also says it does not recognise this deal.

According to Koseoglu, the group says it does not want the Russians patrolling along the M4 highway. In the past, Russia has cited HTS's presence as the reason for attacking areas in Idlib.

Nine years of war

The Russia-backed government offensive on Idlib sparked what the United Nations said may be the worst humanitarian crisis yet in a war that has driven millions from their homes and killed hundreds of thousands.

At least 900,000 people were driven from their homes since last December, many of whom had amassed near the border with Turkey seeking relative safety.

Russia had repeatedly played down any talk of a refugee crisis and accused Turkey of violating international law by pouring troops and equipment into Idlib since early last month.

About 60 Turkish troops have been killed in that time.

Sunday's patrols come as Syria's war enters its 10th year. What started as peaceful protests on March 15, 2011, to topple Syrian President Bashar al-Assad's rule quickly turned into a bloody conflict that has seen the interventions of foreign powers.

Nine years on, al-Assad remains in power after gaining back large swaths of land from opposition factions in Syria.