Turkey vowed on Thursday that it would continue with its operation against Kurdish factions in Syria’s Afrin region, calling on the US to “stop supporting terrorists.”
"Those who support the terrorist organization will become a target in this battle," Deputy Prime Minister Bekir Bozdag told broadcaster A Haber in an interview.
"The United States needs to review its solders and elements giving support to terrorists on the ground in a way to avoid a confrontation with Turkey."
The Turkish offensive against the People’s Protection Units (YPG) has seen Washington's fellow NATO member Ankara attacking a US-allied force, even raising fears of military confrontation between the two Alliance powers.
Turkey said it has made gradual progress in the offensive against the YPG, but has refused to give any time limit for the campaign.
Turkish Prime Minister Binali Yildirim hit out at the US "support for terror organizations", which "could not be accepted".
"The country we call an 'ally' in NATO is in cahoots with terror organizations," he said in a speech in Ankara.
"This is a grave and very painful situation. For a country like America to work with terror organizations is really very humiliating," Yildirim said.
Turkish President Recep Tayyip Erdogan and US President Donald Trump spoke late on Wednesday to tackle the situation in Afrin.
The White House said Trump had urged Ankara to "to de-escalate, limit its military actions", expressing concern that the assault could harm the fight against extremists.
But a Turkish official said the US statement did "not accurately reflect the content" of the call, adding that Trump did not share any concerns regarding "escalating violence".
Ankara views the YPG as a terror group linked to the outlawed Kurdistan Workers' Party (PKK) inside Turkey. The PKK is blacklisted by Ankara and its Western allies. But the YPG is still working closely with Washington against the ISIS extremist group in Syria, in defiance of Turkey's warnings.
In a move that could further raise the stakes, Erdogan on Wednesday raised the prospect of an operation on Manbij, a YPG-held town to the east, where there is a US military presence.
Following the Erdogan-Trump telephone talks, the US envoy to the coalition against ISIS, Brett McGurk, said on Twitter the "prolonged operation risks giving life to ISIS as it's on verge of defeat".
"The US (is) now engaged intensively to urge restraint and de-escalation. We are prepared to work with Turkey on legitimate security concerns," he added.
Washington has more than 2,000 special forces and support troops inside Syria, mainly east of the Euphrates in an area also controlled by the YPG but separate from Afrin, which is west of the river.
In response to Erdogan's call on the US to stop supplying weapons to the YPG, Trump told the Turkish leader that "his country no longer supplied the group... and pledged not to resume" weapons delivery, the official said.
Trump also expressed concern about "the destructive and false" anti-American rhetoric emanating from Turkey, the White House said.
But the Turkish official said Trump "did not use the phrase 'destructive and false rhetoric coming from Turkey'", adding Trump said "open criticism" of the US "raised concerns".
As the operation entered its sixth day, an AFP correspondent saw tanks on the Turkish side of the border and soldiers ready to go into Syria amid tight security.
Turkish artillery fire pounded Afrin, state-run news agency Anadolu said.
Yildirim said over "300 terror organization members were neutralized".