A delegation from the US arrived in Turkey this week to begin working on a buffer zone in northern Syria, under a plan strongly rejected by Damascus.
Turkish and American officials struck a deal last week to establish the safe zone after tension between Ankara and Kurdish forces backed by America in Syria.
But Damascus has accused the two of breaching its sovereignty with an expansionist and aggressive project.
The Turkish Defence Ministry said six US officials arrived in the south-eastern city of Sanliurfa on Monday to start setting up a joint operations centre that will open "in the coming days".
There has been cautious progress on the centre despite other disputes straining relations, including Turkey's purchase of the Russian S-400 missile defence system and trials of US consulate employees in Turkey on terrorism charges.
No details have been provided on the size or timetable for the zone, but the deal appears to have provided some breathing space after Turkey had threatened an imminent attack on the Kurdish People's Protection Units, which control a large area of northern Syria.
The YPG has been a major US ally in the fight against ISIS in Syria, but Ankara considers them terrorists and an offshoot of the Kurdistan Workers' Party, which has fought a bloody insurgency in Turkey for 35 years.
Turkey has called for the safe zone to be 30 kilometres wide — a demand repeated by Defence Minister Hulusi Akar on Monday.
"We have said on every occasion that we need a width of 30 to 40km," Mr Akar told state-run TRT television.
Ankara has threatened militarily action if the US fails to agree on a solution that will protect the border with Syria.
The Kurds have agreed to a buffer zone but have requested for it to be 5 kilometres wide, which was rejected by Turkey.
While fighting ISIS, the Kurds have taken advantage of the Syrian war to set up an autonomous region in the north-east.
But as the fight against ISIS winds down, the prospect of a US military withdrawal has stoked Kurdish fears of a long-threatened Turkish attack.
Kurdish forces have been building defences against a Turkish incursion, digging large tunnels and lining them with concrete.
Turkey has already carried out two cross-border offensives into Syria in 2016 and last year.
In the second, it and allied Syrian rebels overran the Kurdish enclave of Afrin in the north-west.
