Turkish and US officials struck a deal last week to establish the safe zone to manage tensions between Turkey and US-backed Kurdish forces in war-torn Syria.
But Damascus has accused Ankara and Washington of violating its sovereignty with the "expansionist" and "aggressive" project.
Turkey's defence ministry said that six US officials arrived in the southeastern city of Sanliurfa on Monday to start setting up a joint operations centre, which is to open "in the coming days".
No details have been provided on the size or timetable for the safe zone, but the deal appears to have provided some breathing room after Turkey had threatened an imminent attack on the Kurdish People's Protection Units (YPG), which control a large swathe of northern Syria.
The YPG has been a key US ally in the fight against the Islamic State group in Syria, but Ankara brands them "terrorists", viewing them as an offshoot of the Kurdistan Workers Party (PKK) which has fought a bloody insurgency inside Turkey for 35 years.
Turkey has called for the safe zone to be 30 kilometres (18 miles) wide -- a demand reiterated by Defence Minister Hulusi Akar on Monday.
"We have said on every occasion that we need a width of 30 to 40 kilometres," Akar told state-run TRT television.
The Kurds have agreed to a buffer zone, but have requested it to be five kilometres wide, a proposal rejected by Turkey.
While fighting IS, the Kurds have taken advantage of the Syrian war to set up an autonomous region in the northeast.
But as the fight against IS winds down in the region, the prospect of a US military withdrawal has stoked Kurdish fears of a long threatened Turkish attack.
Turkey has already carried out two cross-border offensives into Syria in 2016 and 2018, the second of which saw it and allied Syrian rebels overrun the Kurdish enclave of Afrin in the northwest.
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