The 19-year-old has been in training with the Celtic first team over the past few days and joins Jos Hooiveld and Ki Sung-Yueng as January arrivals.

The Celtic boss, though, categorised Rogne along with fellow youngsters Josh Thompson and Milan Misun, whom he sees as part of the club's long-term future.

Mowbray, who rejected one report claiming he had told midfield star Scott Brown he wanted to sell him, told the club's official website: "Thomas is a young player we've watched for a while and we're delighted to bring him to the club.

"He's only 19 but has had good experience in the Norwegian league.

"We've had a chance to have a look at him in recent days at Lennoxtown and he's shown up well.

"He has all the physical attributes and personality to be a success at Celtic.

"Thomas has a bright future and will be training with the first-team squad, and competing for a place in the side.

"Like Josh Thompson and Milan Misun, Thomas is a big part of our future plans in defence.

"We are bringing these talented players to the club in order to ensure the foundations are in place for the coming years."

Rogne, though, is looking to force his way into the first team at Parkhead sooner rather than later.

"I'm absolutely delighted to sign for a club of Celtic's stature," he said.

"It really is a dream come true to join such a famous club.

"I've already joined training with the first-team for the last few days and I have received a great welcome and have enjoyed very much working with the manager and players at Celtic.

"The Celtic first team is where I want to be and I'll be doing my very best to try and make an impact and ensure that I can achieve this as soon as possible."

On the subject of Brown, Mowbray claimed the Scotland midfielder is still an integral part of his plans despite a report claiming that in a meeting between the two men before Christmas, the Hoops' boss had informed the 24-year-old of his plan to sell him.

As the Parkhead club revealed they are currently taking legal advice over the issue, the former Hibernian and West Brom manager said: "The story is absolute nonsense. I never told Scott Brown that I want him to leave the club.

"Scott is a huge player for Celtic and absolutely part of the future plans of this club.

"I have worked with Scott for a number of years and have a great relationship with him.

"It's disappointing that people are able to write things which are so inaccurate but I know our supporters will understand that unfortunately this is one of the things we need to deal with.

"I am sure they will also know that we are all working together at Celtic to do all we can to achieve success for the club."