Turkey's Defense Minister Nurettin Canikli says Turkey has begun a military operation against U.S.-backed Kurdish fighters in Syria's Afrin region.
Canikli said the military operation that Ankara has been prepared began "de facto" on January 19 with cross-border shelling by Turkish forces inside Turkey.
Canikli said Ankara had "no option" and must "clear all terrorist elements" from northern Syria, which shares a border with Turkey.
He also said Ankara and Moscow would "continue" talks about the military operation.
A spokesman for U.S.-backed Kurdish People's Protection Units (YPG) confirmed that Turkish forces began heavily shelling Syria's Afrin region from Turkish territory on January 19 shortly after midnight.
The spokesman said Turkey was targeting Kurdish villages, and that YPG fighters would "respond with utmost force" to any attack on Afrin.
The fighting comes a day after Turkish Foreign Minister Mevlult Cavusoglu announced that Ankara would coordinate with Moscow and Tehran on air operations in Syria’s Afrin region.
The state-run Anadolu news agency reported on January 18 that Turkish security forces were preparing for intervention in Syria's Kurdish-held regions of Afrin and Manbij.
It said tanks had been deployed in Turkey's Eastern Mediterranean coastal province of Hatay in response to "a border security threat."
Anadolu also said a National Security Council meeting headed by Turkish President Recep Tayyip Erdogan concluded that Turkey should take "immediate" and "resolute" steps to protect itself from threats emanating out of western Syria.
'Army Of Terror'
On January 15, Erdogan threatened to crush a "army of terror" he claims the United States is trying to set up on Turkey’s border with Syria.
Ankara is angry that Washington is allied with the Kurdish YPG forces that have been fighting against Islamic State militants in Syria.
Turkey considers the YPG to be a terrorist organization.
Turkey's government was infuriated by a January 14 statement from the U.S.-led coalition in Syria that said Washington would help set up a new 30,000-strong border force in Syria that includes the YPG.
U.S. Secretary of State Rex Tillerson says he told Cavusoglu on January 17 that the "entire situation has been misportrayed" and "misdescribed" by "some people" who “misspoke."
Tillerson said the United States aims to provide training to local elements in Syria -- not create a new border security force.
But Cavusoglu said Ankara was "not completely satisfied" with Tillerson’s explanation, adding that Turkey's "mistrust" of Washington continues.