UEFA has punished Champions League participants Olympiakos and Zenit St. Petersburg for the racist behaviour of their fans by ordering stadium sections closed at last-16 matches.

UEFA said the lower tier of the north stand at Karaiskakis Stadium will be empty when Olympiakos hosts Manchester United on Feb. 25. The section of Zenit's Petrovsky Stadium where ultras gather will be closed when Borussia Dortmund visits the same day.

Olympiakos was punished for "racist conduct of supporters" and setting off fireworks during a Dec. 10 group match against Anderlecht. UEFA fined the Greek club €30,000 ($41,250).

UEFA had charged Zenit for fans displaying a racist banner, throwing fireworks and crowd disturbances at Austria Vienna on Dec. 11. Zenit was fined €40,000 ($55,000).

Zenit said in a statement that the club was threatened with a stronger sanction because of the poor reputation of its fans.

"Due to the numerous violations by the club's fans in other UEFA matches, the commission considered the possibility of implementing even more severe sanctions against Zenit, namely the complete closure of the stadium," the Russian club said.

The clubs can appeal the sanctions.