FIFA on Thursday dismissed appeals by Real Madrid and Atletico Madrid against a ban on registering new players in the next two transfer windows for irregularities in the signing of foreign players under 18.

Real, who called the ruling "profoundly unfair", and Atletico were also fined 360,000 and 900,000 Swiss Francs respectively.

However, the two Spanish giants -- last season's Champions League finalists -- have announced they will launch a final appeal to the Court of Arbitration for Sport (CAS).

"The FIFA Appeal Committee has decided to reject the appeals lodged by Spanish clubs Atletico de Madrid and Real Madrid and to confirm in their entirety the decisions rendered by the FIFA Disciplinary Committee in the respective cases relating to the protection of minors," FIFA said in a statement.

Both clubs were sanctioned in January, but by appealing had temporarily held off the ban during the transfer window which closed last month.

They will now not be able to register any new players in either of the next two windows, in January 2017 and July-August 2017, before being able to do so once again in January 2018.

Barcelona served a similar ban in 2015, with an appeal to CAS proving unsuccessful in their case.

European champions Real responded by saying they will now go to the CAS in an attempt to have the decision overturned "as quickly as possible".

"The club regrets the decision on the ground that it is profoundly unfair and contrary to the most elementary principles of penal law," read a statement posted on their website.

"The club will begin the appropriate appeals procedure before the Court of Arbitration for Sport, requesting that the decision be completely overturned, with absolute confidence that said organisation will come to an entirely favourable decision.

"Real Madrid will request that the procedure be undertaken in an urgent manner in order to obtain a decision from the CAS as quickly as possible."

Under international football rules, players under 18 cannot be transferred to another country, except in limited circumstances, and all transfers need the approval of a special FIFA committee.

Atletico insisted they had such clearance from FIFA for the players under investigation.

"Our club does not agree with the ruling and therefore has decided to appeal before the Court of Arbitration for Sport," Atletico said in a statement.

"Our organisation wishes to state that one hundred percent of the licenses of our players who are part of this investigation and continue at the club have been regularised by FIFA itself, receiving authorisation from the sub-committee to process the license and compete in different (under-age) categories."

Atletico used the close-season window to make several new signings, while Real had an uncharacteristically quiet window.