Erdogan threatened on Monday to “strangle” a planned 30,000-strong US-backed force in Syria “before it’s even born,” as Washington’s backing for Kurdish fighters drove a wedge into relations with one of its main Middle East allies, Reuters reported.

This comes after, the United States announced its support on Sunday for plans for a “border force” to defend territory held by US-backed, Kurdish-led fighters in northern Syria.

The Syrian government of President Bashar al-Assad responded on Monday by vowing to crush the new force and drive US troops from the country. 

Assad’s ally Russia called the plans a plot to dismember Syria and place part of it under US control.

But the strongest denunciation came from Erdogan, who has presided as relations between the United States and its biggest Muslim ally within NATO have stretched to the breaking point, reported Reuters.

“A country we call an ally is insisting on forming a terror army on our borders,” Erdogan said of the United States in a speech in Ankara. “What can that terror army target but Turkey?”

“Our mission is to strangle it before it’s even born.”

Erdogan said Turkey had completed preparations for an operation in Kurdish-held territory in northern Syria.

The Kurdish-led regions in Syria say they need the border force to protect them against threats from Ankara and Damascus.

“To prevent any attack... there must be a deterrent force that protects the border between our areas and the others,” Fawza Youssef, a senior Kurdish politician, told Reuters.

“Until a political settlement is reached in Syria, these areas need protection. Now, there aren’t any guarantees,” she said.

The United States has led an international coalition using air strikes and special forces troops to aid fighters on the ground battling Daesh militants in Syria since 2014. It has about 2,000 troops on the ground in Syria.