Update (8.55 p.m. EDT): Costa Cruises has confirmed that Costa Fascinosa left Tunis port at 1:55 a.m. According to its statement, the captain reported that 13 passengers had not returned to the ship. The company and its care team are continuing to work with local authorities, and three additional care team members are expected to arrive in Tunis tomorrow to offer assistance.

MSC Cruises said the return of passengers to MSC Splendida is still undergoing. The company is in contact with approximately 50 countries whose nationalities were onboard in an effort to receive relevant information, it said in a statement. MSC has made onboard Internet and telephone services free of charge to ensure passengers are able to contact home. The ship remains in La Goulette; a departure time has not yet been determined.

Update (6:15 p.m. EDT): Costa Cruises said 14 of its passengers on Fascinosa have not returned to the ship. The cruise line is providing complete assistance to all passengers and their relatives, it said in a statement. The ship is expected to disembark La Goulette at 12:30 a.m., upon clearance.

Update (2:43 p.m. EDT): Costa Cruises has confirmed Costa Fascinosa will depart Tunis tomorrow, March 19, although an exact time has yet to be determined. The ship was originally scheduled to disembark at 7 p.m. tonight.

(1:45 p.m. EDT) -- Cruise passengers were on shore excursions at the Bardo National Museum in Tunisia at the time of today's terrorist attack; it is still unclear, however, whether any of them were among the tourists killed.

Both Costa Cruises and MSC Cruises have ships -- Costa Fascinosa and MSC Splendida -- currently docked in La Goulette, Tunisia. At the time of the attacks, some of MSC's passengers were on shore excursions that included a stop at the museum, which is one of the country's major tourist attractions. Costa also confirmed that some its 3,161 passengers were on a shore excursion in the city.

While details are still emerging, the international press is painting a frightening scenario. CBS is reporting  that the attackers waited for four tour buses to arrive at the museum before opening fire (a photo published by the Daily Mail shows a Costa tour bus with a bullet hole in it). CNN has reported that gunmen entered the museum and created a hostage siege.

While two of the gunmen were killed by Tunisian security forces, another three gunmen are still being sought, the network said.

The death toll from the attack continues to rise. The New York Times has reported that at least 17 foreign tourists were killed, including those from Poland, Italy, Germany and Spain. CNN has reported that another 20 tourists were wounded.

As soon as the ships' commands were notified of the attacks, all shore excursions were recalled back to both ships with all ground activities suspended, according to the cruise lines. Extra security measures have been put around the port to ensure the security of the ship, its passengers and crew, Costa said.

Costa Fascinosa, which had been sailing a seven-night Western Mediterranean itinerary embarking in Genoa on March 15, was scheduled to depart Tunis tonight at 7 p.m.; that will be delayed, the company said. Members of the Italian cruise line's management and care team are traveling to Tunis to meet with local authorities and passengers onboard.

MSC Splendida carries 3,274 passengers. It embarked from Barcelona on March 13 on a Western Med itinerary.  

Tunisia was one of the seats of violence during the Arab Spring in early 2011; however, it had seemingly weathered the surge of extremist governments in the region and had their first democratic election in December. CNN noted, however, that the country has had a high number of people traveling to Iraq and Syria in conjunction with ISIS.

Cruise Critic will continue to monitor this breaking news story.

--By Chris Gray Faust, Destinations Editor

Related content:

Cruise Lines Cancel All Calls to Tunisia Following Terrorist Attacks

13 Cruise Passengers Confirmed Dead in Terrorist Attack; More Missing

Cruise Critic Members React to Tunis Attack