Turkey and the US have become embroiled in a consular row, mutually scaling back visa services.
The American mission in Ankara said it had suspended all non-immigrant visa services in order to “reassess” Turkey’s commitment to staff security.
Turkey’s embassy in Washington replied by suspending “all visa services”.
The latest spat began when a US consulate worker in Istanbul was held over suspected links to a cleric blamed for last year’s failed coup in Turkey.
Washington condemned the move as baseless and damaging to bilateral relations.
The arrested consulate employee was a male Turkish citizen, Turkey’s state-run Anadolu news agency reported.
The row prompted a 4% fall in Turkey’s main share index while the Turkish lira tumbled more than 2.5% against the dollar.
In itson Sunday, the US embassy in Ankara said: “Recent events have forced the United States government to reassess the commitment of government of Turkey to the security of US mission and personnel.
“In order to minimise the number of visitors to our embassy and consulates while this assessment proceeds, effective immediately we have suspended all non-immigrant visa services at all US diplomatic facilities in Turkey.”
Only people permanently moving to the US will now be able to apply for visas.
Turkey accused of holding detainees hostage
Mark Lowen, BBC News, Istanbul
Turkey stands accused of holding detainees as hostages in its bilateral disputes with countries.
As well as the consular employee, an American pastor was arrested here a year ago. Several German nationals are also in custody as Ankara presses the US to extradite the cleric it accuses of masterminding the coup, and urges Berlin to deport Turkish citizens who have claimed asylum there.
Germany has already warned its nationals against travelling to Turkey.
There could now be a similar response from Washington in this unprecedented row.
Themimicked the American one, but said that “effective immediately we have suspended all visa services regarding the US citizens at our diplomatic and consular missions in the US”.
It added: “This measure will apply to sticker visas as well as e-visas and border visas.”
Ankara has for months been pressing Washington to extradite US-based cleric Fethullah Gulen over his alleged role in the botched coup in July 2016.
Turkish President Recep Tayyip Erdogan accuses Mr Gulen of instigating the unrest – a charge the cleric denies.
In the aftermath of the coup attempt, which was led by military officers, 40,000 people were arrested and 120,000 sacked or suspended.
The new diplomatic low between the US and Turkey comes less than a month after Donald Trump said ties between the countries were “close as we’ve ever been”.