The United States is asking the Turkish government to present evidence to back up its accusations used to justify the detention of locally-employed U.S. consulate members and several American citizens, including jailed American pastor Andrew Brunson.
"We would call upon the government of Turkey to please provide us that evidence, if there is evidence, that they were involved in what Turkey alleges, and that is terrorism," said State Department spokesperson Heather Nauert on Thursday.
She told reporters the U.S. has "not seen any evidence" to that effect and called on Ankara to fulfill its pledge to allow access for the detained to see their lawyers.
On Wednesday, Secretary of State Rex Tillerson spoke with Turkish Foreign Minister Mevlut Cavusoglu, conveying Washington's "profound concern" over the detentions. It is the second phone call in less than a week between the top diplomats of two NATO allies.
Relations between Turkey and the U.S. are deeply strained following last week's arrest of local U.S. consulate employee Metin Topuz on terrorism and espionage charges, in relation to a failed coup staged last year against Turkish President Recep Tayyip Erdogan. Both countries have severely restricted the issuance of non-immigrant visas.
Washington's suspicions are growing that the detention of local staffers could be politically driven.
Meanwhile, about a dozen U.S. citizens have been held in connection with last year's failed coup, including Brunson, who has been in jail without being charged for about a year.
"It is something that we follow extremely closely. We would like to see Pastor Brunson brought home," Nauert said Thursday. "That's one of the issues that is consistently brought up, the safety, the welfare, the well-being of the American pastor, Pastor Brunson."
Tillerson raised Brunson's case over the weekend in his phone call with Cavusoglu, according to the State Department.
Erdogan had said that if the U.S. wants Brunson freed, it should extradite Muslim cleric Fethullah Gulen, whom Ankara blames for last year's failed coup attempt.
While Washington and Ankara agreed the two sides would remain in close contact to calm the escalated tension, there appeared to be little sign of a quick resolution to the diplomatic dispute.
Erdogan: US 'sacrificing' ties with Turkey
On Thursday, Erdogan said the United States is "sacrificing" ties between the two allies.
"It is unacceptable for America to sacrifice a strategic partner like Turkey for an impertinent ambassador," Erdogan said, referring to Washington's ambassador to Ankara John Bass, who is due to leave his post later this week for a new assignment in Afghanistan.
Following Topuz's arrest, the U.S. Embassy in Ankara announced it would temporarily halt all non-immigrant visa applications — a move that was quickly mirrored by Turkey.
Erdogan blamed Bass for the tensions, having declared that the ambassador would no longer be considered Washington's legitimate representative.
But Washington has strongly backed the American ambassador's actions, reiterating its criticism of the detention of its local employee. Observers suggest the move has closed the door to Ankara's hopes of ending the crisis by blaming it on Bass, rather than Washington.
"We're actually quite surprised by the United States State Department response to what would be considered as a routine investigation," Turkish Deputy Prime Minister Mehmet Simsek said during a visit to Washington on Wednesday.
"We think the reaction is out of context and we hope that pretty soon this issue will be resolved," Simsek said. "U.S. and Turkey have been friends, allies, partners, for over half a century. And that relationship, this partnership, I think, is strong enough to weather such crisis."
Esha Sarai and VOA Turkish contributed to this report.