Turkish diplomatic sources said the passage of the first ship through the Bosphorus due on Wednesday did not take place.

Anadolu state news agency said both deployments, scheduled for Wednesday and Thursday, have been cancelled with Ankara not yet informed of any possible rescheduling.

Last week Turkey announced that it had been informed through diplomatic channels that two US warships "will pass toward the Black Sea" and remain in the region until May 4.

There was no confirmation from Washington either of the planned deployments or of their cancellation.

Washington is required to give Ankara at least 15 days notice before sending warships through the Bosphorus and Dardanelles straits under the terms of the 1936 Montreux Convention.

The treaty's terms allow foreign warships to stay in the Black Sea for 21 days.

US Navy ships routinely operate in the region in support of Ukraine, which has been fighting Russian-backed forces in its east since a 2014 revolution ousted the pro-Moscow leader in Kiev.

Russia annexed Ukraine's Crimea peninsula around the same time, setting up a confrontation with the West that lingers to this day.

Last week's announcement of a US deployment of warships came as tensions between Moscow and Kiev have risen due to a build-up of Russian troops at the Ukraine border.

These troop deployments come against the backdrop of renewed incidents between Kiev forces and pro-Russian separatists in eastern Ukraine.

Wednesday's news of the cancellation of the US warships' deployment came a day after US President Joe Biden talked by phone with his Russian counterpart Vladimir Putin.

During that conversation, Biden proposed a summit with Putin in a neutral country and called on Russia to "de-escalate tensions", according to the White House.