U.S. WARNING
U.S. and Turkish troops have so far carried out half a dozen joint air missions over northeast Syria and two land patrols.
The NATO allies disagree over the depth of the zone and who should control it, while the United States avoids even referring to a "safe zone", talking instead of a "security mechanism".
The United States has warned Turkey that unilateral action would not serve any country's security.
"The last thing Turkey would like is an unintended clash with the U.S. troops on the ground," said Ozgur Unluhisarcikli, of the German Marshall Fund in Ankara.
Instead, he said Turkey could adopt a "graduated strategy" and continue negotiating with Washington while making incursions in areas where there are no U.S. troops and few YPG terrorists.
Even so, Ankara would be wary of the political consequences in Washington, where Trump's public support for Erdogan is set against demands in Congress for sanctions on Ankara over its purchase in July of Russian S-400 missile defence systems.
Cavusoglu said Ankara would move in stages - from joint patrols to "going inside and clearing out the terrorists", then establishing facilities for its forces inside Syria followed by "the humanitarian aspect and return of refugees".
Turkey's allies have yet to set out their response, but are unlikely to offer financial support for any operation which settles people hundreds of kilometres from their homes and alters the demographics of northeast Syria.
Erdogan, who has supported opposition fighters against Syrian President Bashar al-Assad, will also face opposition from Assad's most powerful backers Russia and Iran. Russia has pointed to a 1998 security agreement between Turkey and Syria, suggesting Erdogan should accept the Damascus government's authority in the area.
