Amid growing international concern over the four-day-old cross-border campaign into Turkey's neighbour, President Recep Tayyip Erdogan vowed that Ankara would emerge victorious.
Turkey on Saturday launched operation "Olive Branch" aimed at rooting out the Kurdish People's Protection Units (YPG) militia, which Ankara sees as a terror group, from its Afrin enclave in northern Syria.
The campaign has caused ripples of concern among Turkey's NATO allies, especially the United States which is still working closely with the YPG to defeat Islamic State (IS) jihadists in Syria.
Mattis, on a visit to Indonesia, warned the offensive "disrupts what was a relatively stable area in Syria and distracts from the international effort to defeat" IS.
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US President Donald Trump is expected to express America's unease in a call telephone with Erdogan tomorrow.
French President Emmanuel Macron joined in the chorus of concern when he spoke by phone to the Turkish leader today.
"While recognising Turkey's security needs, Macron "told his Turkish counterpart of his concern over the military intervention," the French presidency said.