Turkish President Recep Tayyip Erdogan on Wednesday warned he will launch a new operation in Syria within days against the U.S.-led Coalition backed People’s Protection Units (YPG) militia that Ankara considers a terrorist group, risking renewed tensions with its NATO ally.

Washington’s relationship with the predominately Kurdish YPG, a key partner spearheading the fight against Islamic State in Syria, is a major bone of contention between the U.S. and Turkey.

Turkey has repeatedly lambasted Washington for providing military support to the militia and threatened to attack areas held by the YPG.

Erdogan announced the plans for a new offensive a day after the Pentagon said observation posts were in place on the Syria-Turkey border to prevent altercations between the Turkish army and the YPG.

The YPG is considered by the Turkish government to be inextricably linked to the outlawed Kurdistan Workers’ Party (PKK), which has waged a decades-long insurgency in Turkey, and is designated as a terror group by Turkey and its Western allies.

But the YPG is not a proscribed organization in the United Kingdom, United States or European Union, and it is a key component of the Coalition-backed Syrian Democratic Forces alliance which is waging the campaign against ISIS in Syria.

“We will start an operation to free the east of the Euphrates from the separatist terrorist organization in the next few days,” Erdogan said during a speech in Ankara, referring to territory held by the SDF.

“The target is never American soldiers but terrorist organization members active in the region,” Erdogan told the audience at a defense industry summit.

The Pentagon on Tuesday announced the posts’ establishment on the northeast Syria border region despite calls from Ankara not to go ahead with the move.

New administrative arrangements in areas of northern Syria under SDF control were formalized in 2016 with the creation of the Democratic Federation of Northern Syria, but Turkey refuses to recognize the territory on its border.

Erdogan claimed Turkey was not being protected from terrorists but “terrorists were being protected” from possible action by Turkey.

The SDF announced on October 31 it was suspending its operation against ISIS after Turkey fired across the border at militia posts in northern Syria over a period of days in late October and early November.

In an attempt to defuse tensions, U.S. troops carried out patrols in DFNS territories targeted by Turkey.

Youssef Hammoud, spokesperson for the National Army, a Turkey-backed Syrian rebel alliance, said the aim of a new operation would be to remove the YPG from an area spanning Manbij to Tal Abyad.

‘Delaying tactic’ in Manbij

Coalition forces have worked closely with the YPG under the SDF alliance against the ISIS.

U.S. forces have joined the SDF east of the Euphrates as well as in the flashpoint city of Manbij, west of the river.

In a bid to avoid any clash, the NATO allies agreed a “roadmap” for Manbij in June. In November, Turkish and American troops launched joint patrols in the northern city.

Part of the agreement was that the YPG would leave Manbij and that the NATO allies would work together to establish a local security structure and decide who will govern.

But Erdogan on Wednesday said Turkey “still not got the result it wanted” in Manbij.

“There has been a delaying tactic undeniably used in Manbij, and right now it is still being used,” he said, adding that the threat from ISIS no longer existed in Syria.

Turkey training rebels

Hammoud said the different rebel groups “were informed a while ago” of a possible operation, adding that training supervised by Turkish officers had been underway.

On December 9, Hammoud said that the National Army opened camps to train fighters in preparation for the operation.

Turkey has previously launched two operations in northern Syria. The first offensive, Euphrates Shield, began in August 2016 with Turkish forces supporting Syrian opposition fighters against ISIS and was completed by March 2017.

Then in January 2018, Turkish military forces backed Syrian rebels in Operation Olive Branch to clear the YPG from its northwestern enclave of Efrin.

In March, the operation was completed with the capture of Efrin city.

Erdogan has repeatedly warned Turkey would not allow “a terror corridor” to be formed on its border by the YPG.

Ties between Washington and Ankara have been tense over several issues in recent years including the detention of an American pastor, Andrew Brunson, who was released in October and the failure to extradite Fethullah Gülen, a U.S.-based Muslim preacher blamed for the July 2016 failed coup against Erdogan.

With reporting from AFP