Following Tuesday’s terror attacks in Istanbul in which at least 41 people were killed and hundreds injured, several cruise lines have announced changes to itineraries featuring the Turkish capital.

Turkey has seen six attacks since last December, but the attack by gunmen wearing explosive vests on Ataturk International Airport is the largest incident to hit the capital in recent memory.

Neither the U.K.’s Foreign & Commonwealth Office nor the U.S.’s State Department have altered their travel advice to Turkey, which is usually the trigger for travel companies to cancel or alter travel plans. The U.S. currently has a warning for the southeast part of Turkey bordering Syria and Iraq.

At least 102 cruise ship port calls were scheduled for the remainder of the year at Istanbul at the time of the attack, but now Cruise Arabia & Africa has been informed by several cruise lines visiting the city that they are changing itineraries to avoid Turkey this year.

Celebrity Cruises on Wednesday cancelled all upcoming ship visits to Istanbul, citing Tuesday’s terrorist attack.

Two Celebrity vessels that were scheduled to use Istanbul as an occasional base for Eastern Mediterranean cruises over the next five months instead will operate out of Piraeus, Greece, the port for Athens. Seven sailings are affected.

Also cancelling a visit to Istanbul on Wednesday was luxury line Seabourn. The line said a cruise on the 450-passenger Seabourn Odyssey scheduled to begin Saturday, July 2nd in Istanbul instead would begin in Piraeus.

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“After a very careful and thorough review, Seabourn has decided to replace the July 2, 2016 turn port of Istanbul with Piraeus (Athens),” a spokesperson told Cruise Arabia & Africa. “Seabourn is closely monitoring the situation in Istanbul. The company analyses information regarding safety and security from many sources, which includes liaising with government intelligence agencies and on-the-ground port security assessments.”

Celebrity and Seabourn were among just a handful of cruise operators that still had Istanbul and other Turkish ports on the schedule for 2016. Many lines dropped Turkey calls months ago after an earlier series of terrorist incidents in the country.

Costa Cruises, Crystal Cruises, Disney Cruise Line, MSC Cruises, Norwegian Cruise Line, Regent Seven Seas Cruises and Oceania Cruises all had previously cancelled visits to Turkey for 2016. Costa Cruises was one of the first lines to drop Turkey, possibly as a result of heightened security sensitivity following the terror attack on cruise passengers in Tunisia.

Norwegian, Regent and Oceania also have dropped calls in Turkey for 2017.

Princess Cruises has not adjusted its itinerary for Royal Princess, which is due into Istanbul next Thursday, July 7, but a spokesperson told Cruise Arabia & Africa this was likely to change.

“Safety and security of our guests remains our number one priority, but there are a range of implications to changing a port call and we want to make sure we’re poised to manage it all effectively to deliver the best experience,” he said, adding that a decision would be made Thursday.

Princess Cruises and Seabourn are both owned by Carnival Corporation, which also owns Holland America, which has its new flagship Koningsdam scheduled to visit Istanbul this year.

Holland America did not reply to a request for comment on its plans, but a Carnival Corporation spokesperson said security was a primary concern for all Carnival brands with scheduled port calls in Istanbul.

“We are looking into the situation, and we will work closely with law enforcement and government agencies to assess the issue and make a determination with our brands. Safety is our number one priority, first and foremost, and the safety of our guests always comes first,” he said.

The world’s second-largest cruise line, Royal Caribbean, no longer sends ships to Istanbul but still operates cruises that stop in Kusadasi, Turkey, the gateway to the ancient ruins of Ephesus. A spokesperson for the line said that itinerary was unlikely to change.

The British cruise line Fred Olsen Cruises has not made any changes to its upcoming cruise for Boudicca, which will stay overnight in Istanbul on October 24^th as part of a roundtrip 30-night Mediterranean grand voyage from Liverpool.

A Fred Olsen spokesperson said its decision on whether to change these plans would be led by the UK Foreign Office. “We are in discussions with our Turkish destinations partners and we will be taking advice from the Foreign and Commonwealth Office. At all times, the safety of our guests and crew is of paramount importance,” she said.