(Update: 7:45 a.m. EDT) -- In addition to missing yesterday's scheduled trip to Icy Straight Point, Celebrity has confirmed it will cancel Millennium's scheduled call in Juneau, Alaska, today.

The line did not specify what was causing the mechanical problem in Millennium's propulsion unit. Celebrity also did not say whether the current problem onboard is related to the propulsion problem that forced the ship to alter a cruise last week.

A statement from the line said: "Along with expert consultants, our engineers have been working around the clock to resolve the issue. Upon further investigation, it is clear that our teams need additional time to fully determine the root cause of the problem."

The line said they will be compensating guests for the itinerary changes, but has not yet said what the compensation would be.

(12:15 p.m. EDT, August 19) -- Mechanical problems with a propulsion unit are keeping Celebrity Millennium in port in Ketchikan, less than one week after engine problems stranded the ship in Seward for four days. It is unclear at this time how long the ship will need to remain in port.

Celebrity Cruises confirmed the problem, reports of which began circulating on Cruise Critic last night.

"Due to a mechanical problem in one of Celebrity Millennium's two propulsion units, the ship returned to Ketchikan last night," Cynthia Martinez, director of global corporate communications for Royal Caribbean Cruises Ltd., told Cruise Critic. Royal Caribbean is the parent company of Celebrity.

"The ship is capable of sailing without the affected unit; however, in an abundance of caution, the Captain decided the safer and more prudent action was to return to port to evaluate the issue… While in Ketchikan, our technical teams will make a full inspection of the unit, and assess the need for any necessary repairs."

Martinez did not respond to questions about whether the propulsion problem this week is related to the engine problem last week.

The ship's visit to Icy Strait Point, scheduled for today, has been canceled. Updates on other scheduled ports of call are expected later today.

Celebrity Millennium departed Vancouver on August 16 and is scheduled to call on Ketchikan, Juneau and Skagway before concluding in Seward on August 23.

--by Dori Saltzman, News Editor