Tension continue to rise in the north-west Syrian province of Idlib and a deadly clash between the Syrian regime and the Turkish military last week threatens to result in a serious escalation between the two sides presiding over a demilitarisation zone there.
Despite Turkish warnings to avoid pushing for further gains in Idlib, the province dominated by a former Al Qaeda affiliate, Russia-backed regime forces have pressed a blistering assault since December.
The deadliest encounter was last week when four Turkish soldiers were killed by Syrian regime shelling and Ankara responded with air strikes and artillery fire, killing 35 Syrian troops.
But what is Turkey's presence in the area since the Astana and Sochi agreements that permitted its armed forces to enter Syrian territory?
The deal initially allowed Turkey to establish 12 observation posts. But the de-escalation agreement has faltered over the last year, with the Russian-backed offensive forcing hundreds of thousands of civilians from Idlib to flee towards the Turkish border.
Those posts have now come under threat from the Syrian military. In June, Syrian shelling and mortar fire killed one Turkish solder and wounded three.
Turkey warned the Syrian regime that it would retaliate if those posts were threatened. The position of those posts has not changed.
Last year, Turkey massed tanks and commandos on its border with Syria, as well as armoured cars and howitzers.
It also moved to reinforce the 12 outposts where flare-ups have occurred, and dispatched commando units to reinforce its southern provinces.
But after the recent attacks against Turkish troops, which Damascus says were in retaliation for Turkish shelling, Ankara has now stationed military vehicles including tanks into Idlib itself, ordering the reinforcements on Friday.
It sent 150 military vehicles with commandos and ammunition.
Pictures published by Turkish state news agency Anadolu showed vehicles transporting tanks into Idlib.
The so-called zone, agreed on September 16, 2018, established an area 14.5 to 24 kilometres wide and ordered militants to leave the zone.
Those linked to Al Qaeda's former Syria affiliate refused to leave and the deal was never fully implemented.
It remains unknown how many troops Turkey has in Idlib in total, nor the precise models of its weaponry.
The agreements between Turkey and Russia regarding the zone included the clause that all heavy weaponry be removed from the area, something which has failed to happen as clashes have continued.
Russia allowed the regime to continue its advance along key roads in Idlib, while Turkey boosted its support of armed groups as a way to counter the Syrian regime advances.
Russia is in Syria at the request of the Syrian government, while Turkey is not, although it is co-ordinating its movements with the Russians.
The Assad government, after a series of military victories that have returned most of the country back into its hands, is now attempting to oust Turkey from Idlib and retake the entire province.
