As Russia annexed Crimea and the Ukraine government began to withdraw its military personnel from the peninsula this week, travel suppliers began cancelling visits to Ukraine and Russia, as well as to Crimean destinations.

Cruise lines have begun altering some of their Black Sea sailings to bypass previously scheduled port stops in Odessa, Sevastopol and Yalta.

Windstar, Oceania, MSC, Regent Seven Seas and Azamara have substituted port calls in alternative countries, including Turkey, Romania, Bulgaria and Greece.

Silversea canceled calls to the Crimean peninsula for the April 25 Black Sea sailing of the Silver Wind and for the July 21 departure of the Silver Spirit. However, should the situation in Crimea improve, the line said it would consider returning to its original itineraries.

Viking Cruises has a 12-day Footsteps of the Cossacks river cruise on the 196-passenger Viking Sineus, which sails from Kiev into the heart of the Crimean peninsula, with port stops in Sevastopol and Yalta. But its Ukraine departures begin in May, and the company has yet to decide if it will cancel any sailings.

“Though we know our passengers are paying attention to the developments on the ground, we have not yet seen significant cancellations,” Richard Marnell, Viking’s senior vice president of marketing, wrote in an email.

During a speech earlier this month at a dinner event to celebrate the christening of its latest generation of river cruise ships, Viking Cruises Chairman Torstein Hagen said that while nearly all of Viking’s river cruise capacity through the end of October was sold out, space was still available on its Ukraine sailings.

Many tour operators have already canceled either part or all of their 2014 tour itineraries that include stops in Crimea, offering affected passengers refunds or the option to rebook travel elsewhere.

Globus canceled all 2014 departures of its Ukraine and Crimea tour; Insight Vacations is no longer offering its 12-day Ukraine, Moldova and Crimea tour; and Intrepid Travel has canceled three Ukraine departures through mid-June.