President Recep Tayyip Erdogan has promised to "drown" the Syrian Kurdish border security force being created by the US.
Speaking in Ankara, the strongman leader said his government has a duty "to drown this terrorist force before it is born."
The US-led coalition in Syria has said the group will work to secure areas which have already been liberated from Isis militants along the northern border of the country with Turkey, as well as the eastern border next to Iraq.
The force will comprise 30,000 people and established over several years. Half of it will be created from the existing members of the Syrian Democratic Forces, led by the Kurds.
Turkey has branded the Syrian Kurdish militia a terror group, claiming it works against the Ankara government alongside Kurdish rebels.
At the moment the Syrian Democratic Forces, active on the borders of Turkey and Iraq, hold almost 25% of territory in Syria.