UEFA president Michel Platini set the deadline at separate meetings with Serbia president Boris Tadic and his Croatian counterpart Ivo Josipovic on Thursday.
Both countries said afterwards that they had been warned that their national teams and clubs could be kicked out of international soccer and UEFA gave further details of the meeting, including Platini's comments, on Friday.
"I must stress... that unless UEFA sees positive and clear signs that concrete measures are being taken within this calendar year, there is the serious risk of suspension ," Platini said.
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