Yet executing the operation on the ground - especially against a well-populated urban centre such as Afrin - could prove much harder than making threats in fiery language.
"Some people misspoke. We are not creating a border security force at all", Tillerson said.
He added: "We have informed them [US] we will be intervening in Afrin and we will take action against the threats towards us wherever they come from on the eastern side of the Euphrates, in Manbij or elsewhere".
Turkish troops and Syrian opposition forces attacked a Kurdish enclave in northern Syria on Sunday in their bid to drive a US -allied Kurdish militia from the region.
Turkey-backed Free Syrian Army rebel factions had captured a Kurdish village with no resistance and were clearing landmines, a Turkish official said. The Turkish artillery returned fire, the governor said.
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Anaru Kitchen was in the game early with two catches for New Zealand , off new ball pair Tim Southee and Seth Rance . Talented batsman Babar Azam top-scored for the Men in Green with run-a-ball 41.
Meanwhile, Syrian activists said Turkish military activities near the borders with Afrin have continued, as well as shelling of the outskirts of the town.
Egypt has condemned Turkey's military offensive in a Syrian Turkish enclave, describing it as a breach of Syria's sovereignty.
The military said it had hit 153 targets so far, including shelters and hideouts used by Kurdish militants.
Turkey has intermittently shelled and carried out air strikes against the YPG in the Afrin area, from where fighters have fired rockets into Turkey.
Ankara, however, denied any civilian casualties, with Cavusoglu accusing the YPG of sending out "nonsense propaganda and baseless lies".
The Pentagon says it limits its assistance to the YPG to regions where ISIS is nearby.
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Amid US calls for restraint, Turkish artillery pounded YPG positions while rockets fired from inside Syria slammed into two Turkish border towns, wounding dozens, according to the local governor's office and a witness.
"Turkey will not allow the creation of a terror corridor or a terror army on its borders and is ready to take any steps necessary in this regard", said a statement after a meeting of the National Security Council (MGK) chaired by Erdogan.
Moscow, a military ally of President Bashar al-Assad that operates a major air base in Syria, has not confirmed giving a green light to the campaign - which Syria has strongly objected to - but did not appear to be acting to prevent it.
The PKK is classified as a terrorist organization by the USA and European Union as well as Turkey. Some were in different khaki-colored uniforms, some in jeans and sneakers.
"This is a historic moment in our revolution", Mohammad al-Hamadeen, a senior officer in the FSA forces, told fighters in Azaz on Sunday as they prepared to join the ground offensive. The Russian military is believed to have a presence there.
Turkish Deputy Prime Minister Bekir Bozdag ruled out the risk of a clash with American forces, saying they were not present in the Afrin region.
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Subs: Ruben Castro (for Leon, 72) 5, Ryan Boudebouz (for Garcia, 76) 5, Roberto Camarasa (for Fabian, 87) 5. "He's the best player ever".
But Ankara considers YPG fighters to be "terrorists" linked to the PKK, reported AFP.