President Recep Tayyip Erdogan signaled Turkish forces may soon carry out an attack on a Kurdish stronghold in northwest Syria, a day after the army shelled the area.
Afrin is controlled by a Syrian Kurdish militia known as the YPG. Turkish officials vowed similar action on several occasions past year.
Rojhat Roj, the YPG spokesman in Afrin, told Reuters the shelling was carried out by Turkish forces in Dar Taizaah and Qalat Seman - areas where he said Turkish forces had deployed as part of an agreement with Russian Federation and Iran.
Turkey will interfere "if the terrorists in Afrin do not surrender", Erdogan also said, adding that Turkish forces "are destroying the western wing of this corridor with the Idlib operation".
The U.S. -led coalition confirmed reports Saturday that it will establish a 30,000-strong new border security force with the People's Protection Units (YPG)-led Syrian Democratic Forces (SDF) in Syria, a move that has already angered Turkey.
"In the coming days, God willing, we will continue with the Afrin [operation] that we started first with Euphrates Shield Operation to purge terrorism from our southern borders", Erdogan said in a speech in central Anatolian Tokat province. Turkish troops are stationed in rebel-held territory on both sides of Afrin.
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US President Donald Trump made a decision to arm YPG fighters despite Turkey's objections and a direct appeal from Erdogan at a White House meeting last May.
The issue is among many causing tense relations between Ankara and Washington, though Turkish officials said in November that US President Donald Trump apparently told them Washington would no longer supply weapons to the YPG. Senior Kurdish official Hediye Yusuf wrote on Twitter that the Turkish operation against Afrin is a "violation" of the Syrian people and undermines global efforts to reach a political solution in Syria.
YPG will fight to "defend our gains, our territories", Roj said.
Turkey has been working closely with Russian Federation and Iran to end the almost seven-year Syrian war, despite Moscow and Tehran supporting Syrian President Bashar al-Assad - and Ankara backing the anti-Assad opposition.
Turkey and its Western allies, including the USA, consider the PKK a terrorist organization.
The Turkey-PKK conflict has killed an estimated 40,000 people since 1984, including more than 3,300 state security forces, militants and civilians since the resumption of hostilities in July 2015.