Russian President Vladimir Putin and his Turkish counterpart Recep Tayyip Erdogan hailed Thursday a "significant decrease in tensions" in Syria's Idlib and pledged to continue working together, the Kremlin said.

The two leaders, who last week agreed a ceasefire in Syria's north-western Idlib region, "are satisfied to note a significant decrease in tensions in the Idlib de-escalation zone," the Kremlin said in a statement after Putin and Erdogan spoke by phone.

The two leaders "confirmed the importance of continuing close joint work... to ensure a sustainable ceasefire regime and further stabilisation of the situation," it said.

Moscow and Ankara agreed to a ceasefire that came into force in the Idlib, the last bastion of resistance to Syria's President Bashar al-Assad, on March 6.

The agreement includes joint patrols by Russian and Turkish militaries in the area. Erdogan on Wednesday said the ceasefire has "started to be violated" during "small incidents" and urged Moscow to take measures. But the Russian military said late Wednesday that they have registered no attacks from inside the Idlib zone.

The deal struck between Putin and Erdogan came after an escalation of violence in Idlib, the province where Ankara is battling Moscow-backed government forces. The conflict in Syria has killed more than 380,000 people since 2011 and displaced half of the country's population.