ANKARA/LONDON: Turkish President Recep Tayyip Erdogan Tuesday called on NATO to take a stance against the United States, a fellow ally, over its plans to form a 30,000-strong Kurdish-led border security force in Syria.

Turkey has been threatening to launch a new military offensive in Syria against Syrian Kurdish militias, which Turkey considers to be terrorists because of their affiliation with outlawed Kurdish rebels fighting Turkey.

Erdogan Monday accused the United States of creating an “army of terror” in Syria along the border with Turkey, and vowed to crush the U.S.-backed border force.

Addressing his ruling party’s deputies Tuesday, Erdogan questioned NATO’s stance on the issue, saying, “Hey NATO! You are obliged to take a stance against those who harass and violate the borders of your members.”

NATO’s headquarters described Turkey as “a highly valued ally” and said the alliance was committed to Turkey’s defense. It said however that the alliance did not have a presence on the ground in Syria and that the matter was an issue for the U.S.-led anti-Daesh (ISIS) coalition, which includes dozens of countries.

The coalition has said the new force, expected to reach 30,000 in the next several years, is a key element of its strategy in Syria to prevent the resurgence of Daesh in Syria.

Iran added its voice to criticism of the U.S. plan to form a new border security force, saying it would cause more instability and “add flames” to the war-torn country. Iranian Foreign Ministry spokesperson Bahram Ghasemi said the planned Kurdish-led force would further complicate the conflict in Syria and is a “blatant intervention” in that country’s internal affairs.

Erdogan reiterated Tuesday that Turkey planned an imminent intervention in the Kurdish-controlled enclave of Afrin in northern Syria. Turkey has sent reinforcements to its border in recent weeks and Erdogan said this week that Turkish troops were already firing artillery at Afrin from the border.

Speaking to reporters after his speech to party legislators, Erdogan said Turkey would conduct the operation in Afrin with Turkish-backed Syrian opposition forces, the state-run Anadolu Agency reported.

Asked whether he planned to discuss the Kurdish-led border force with U.S. President Donald Trump, Erdogan said he had no plans to call the U.S. leader. “We discussed the issue before. He said he would get back to me. I won’t call him as long as he does not get back to me,” Anadolu quoted Erdogan as saying.

Russia has also criticized the nascent U.S. force and warned that it could fuel tensions around Afrin.

In other developments, the Syrian opposition called on Trump and the EU to put pressure on President Bashar Assad and his allies Russia and Iran to return to talks to end Syria’s civil war. Syria’s chief opposition negotiator Nasr Hariri said that unless the West forced Assad and his big-power allies to seek peace then Syrian civilians would continue to be killed.

“I would like to ask all those countries that promised they would support the Syrian people and their aspirations for democracy and peace: Why didn’t they fulfill their promises?” Hariri told Reuters in London.

He also said the next round of the so-called Geneva talks on the fate of Syria would take place in late January, probably around Jan. 24-26, in Vienna.

A spokesperson for Hariri said the opposition would attend those talks.

Hariri said it was very unlikely that the Syrian opposition would attend a meeting on Syria organized by Russia in the Black Sea resort of Sochi.

The opposition had received no invitation so far, and no final decision on attendance had been made.

When asked about U.S. plans to help support the 30,000-strong force dominated by the mainly Kurdish-led Syrian Democratic Forces, he said it could lead to Syria’s partition. “What are the benefits of establishing such an army?” he asked. “It will open the door wide for a future struggle in the region. It could open the door to the future partition of Syria.”

Also Tuesday, the U.N. said fighting between government forces and insurgents in northwestern Syria had displaced more than 200,000 people since mid-December, including some who had already fled fighting elsewhere.

Most are heading for safer areas near the Turkish border.