Istanbul: Turkish President Recep Tayyip Erdogan told Russian counterpart Vladimir Putin on Sunday that it was imperative the Kremlin "clear" Kurdish forces from northern Syria.

Erdogan has been threatening to launch a new military incursion into northern Syria to push out Kurdish forces that he blames for a November bomb blast that killed six people in Istanbul.

A 2019 agreement between Moscow and Ankara ended another ground 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 Bashahr al-Assad -- of failing to follow through on the deal.

Erdogan told Putin in a phone call on Sunday that is was "important to clear the (Kurdish fighters) from the border to a depth of at least 30 kilometres," his office said.

Erdogan "stated this was a priority," the Turkish presidency said.

Some of the Kurdish forces are stationed in areas under Russian military control.

Others have been fighting with the United States against jihadists from the Islamic State group.

Both Moscow and Washington have been putting diplomatic pressure on Ankara not to launch a new ground campaign.

Turkey has been pummelling Kurdish positions near the border with artillery fire and drone strikes since November 20 in response to the bomb blast.

But it has not yet poured in any major forces to support ones it already has stationed in the area.

Kurdish groups deny involvement in the Istanbul attack.