Erdogan has been threatening to launch a new incursion into northern Syria to push out Kurdish forces he blames for a November bomb blast that killed six people in Istanbul.A 2019 agreement between Moscow and Ankara ended another offensive by setting up a 30-kilometre (19-mile) "safe zone" to protect Turkey against cross-border attacks from Syrian territory.Erdogan accuses Russia -- a key player in the Syria conflict which backs President Bashar al-Assad -- of failing to follow through on the deal.Erdogan told Putin in a phone call it was "important to clear the (Kurdish fighters) from the border to a depth of at least 30 kilometres," his office said.Turkey has been pummelling Kurdish positions near the border with artillery fire and drone strikes since November 20 in response to the bomb blast."