Key powers involved in Syria's civil war have criticised US plans to help an allied Kurdish-led militia set up a 30,000-strong "border security force".
Turkey's president vowed to "suffocate" efforts to begin training members of the Syrian Democratic Forces (SDF) and create what he called a "terror army".
Ankara considers Kurds fighting for the SDF to be part of a terrorist group.
Syria's government decried the "blatant attack" on its sovereignty, and Russia warned it could lead to partition.
With the help of air strikes from a US-led coalition, the SDF has captured tens of thousands of square kilometres of territory from Islamic State (IS) militants.
