Real Madrid and Atletico Madrid banned from signing any new players for next two transfer windows
FIFA has banned Real Madrid and Atletico Madrid from registering new signings for the next two transfer windows for breaching its rules on the international transfer and registration of players aged under 18.
The ban does not affect the current registration period and does not prevent players leaving either club, but means that after this month's transfer window closes neither Real or Atletico will be able to register any new players until the summer of 2017.
Atletico have also been hit with a 900,000 Swiss francs fine (£620,000) while Real have been fined 360,000 Swiss francs (£250,000).
A FIFA statement read: "The two clubs were found to have violated several provisions concerning the international transfer and first registration of minor players as well as other relevant provisions with regard to the registration and participation of certain players in competitions.
"Additionally, Atletico Madrid and Real Madrid have been fined CHF 900,000 and CHF 360,000 respectively, while both clubs have been issued with a reprimand and given 90 days in which to regularise the situation of all minor players concerned."
Thursday's announcement comes after FIFA punished Barcelona with a year-long ban in April 2014 for the transfer of players under the age of 18.
Barca appealed to both FIFA and the Court of Arbitration for Sport against the ruling but ultimately lost both bids. However, with the ban being suspended while the appeals were ongoing Barca were able to sign six players, including Luis Suarez, in the summer of 2014.
The Catalan club eventually served their punishment during the two transfer windows in 2015, but they were still able to sign Arda Turan and Aleix Vidal from Atletico Madrid and Sevilla respectively for a combined fee of £37million last summer.
Barca were not able to register Turan and Vidal as players until this month, though, and the duo have only recently been able to make their debuts for the club.
A FIFA spokesperson confirmed to Press Association Sport that Real and Atletico would also be able to sign new players during their bans, but would not be able to register them.
The spokesperson said: "The ban does not prevent the clubs from signing contracts with new players, as long as the players are not being registered to play for the club."
The sanctions against the Madrid clubs follow investigations initially conducted by FIFA's transfer matching system officials and then by FIFA's disciplinary committee.
The FIFA statement added: "The investigations concerned minor players who were involved and participated in competitions with the clubs over various periods between 2007 and 2014 (Atletico Madrid) and between 2005 and 2014 (Real Madrid)."
Atletico have already announced they intend to appeal against FIFA's punishment.
A club statement read: "Our club is not in agreement with the sanction from international football's governing body and will study all the documentation we've received to present an appeal against the sanction."