Turkey’s president has warned of imminent military offensives on two Kurdish-held areas in northern Syria, as tanks and troops mass on the border.
Recep Tayyip Erdogan said Syrian rebels would support Turkish efforts to clear the “terror nests” of Afrin and Manbij.
The areas are controlled by the Kurdish People’s Protection Units (YPG), which Ankara considers a terrorist group.
Earlier, the Turkish army shelled Afrin from positions in the neighbouring rebel-held Syrian province of Idlib.
The Kurdish official in charge of defending the area, Bahjat Abdo, said the bombardment showed “the bankruptcy of Turkish policies in the face of resistance by the people of Afrin”.
“Turkey is aware about the fact that entering Afrin will not be easy because it was the people of Afrin who turned this region into a graveyard for Turkey-backed extremist mercenaries,” he told the ANHA news agency.
Kurdish media say the Afrin enclave, which is north-west of the city of Aleppo and covers about 2,300 sq km (900 sq miles), is home to as many as 500,000 people.
Turkey’s president has for months been threatening to launch an assault on Afrin.
His government considers the YPG an extension of the banned Kurdistan Workers’ Party (PKK), which has fought for Kurdish autonomy in Turkey for three decades.
Turkish officials have watched in alarm over the past six years of civil war in Syria as the YPG and the US-backed Syrian Democratic Forces (SDF) alliance that it dominates have taken control of tens of thousands of square kilometres of territory.
In 2016, Turkey supported an offensive by Syrian rebels – dubbed Operation Euphrates Shield – to drive Islamic State (IS) militants out of the key towns of Jarablus and al-Bab, and also to stop YPG fighters moving westwards towards Afrin and taking full control of the Turkish border.
Although the rebels halted the YPG advance, the US deployed troops around the predominantly Arab town of Manbij to dissuade them trying to take it by force.
The YPG later agreed to withdraw its fighters from Manbij and move them east of the River Euphrates, but Turkish officials say that has not yet happened.
Last October, Turkey stepped up the pressure on the Kurds in Afrin by deploying troops to northern Idlib province as part of a deal agreed with Russia and Iran that set up a “de-escalation zone” with the aim of reducing fighting between rebel factions and Syrian pro-government forces.
On Tuesday, Mr Erdogan told a meeting of his AK Party that Operation Euphrates Shield “drove a dagger into the heart of the game played in Syria” by the Kurds.
“We will soon also destroy one-by-one the other nests of terror in Syria, starting with Afrin and Manbij,” he vowed.
“Those who stabbed us in the back and appear to be our allies… cannot prevent it,” he added, apparently referring to the US.
Mr Erdogan also urged Nato to stop the US helping the SDF create a “border security force” to protect its territory in Syria.
The US plans to train about 30,000 personnel to help prevent infiltration by IS militants across the Turkish and Iraqi borders and the River Euphrates, which effectively divides Kurdish- and Syrian government-held regions.
On Monday, the Turkish president accused the US of “creating a terror army” and said it was the duty of his government to “suffocate” the force.