UEFA set fan deadline for Serbia and Croatia
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 football 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 for the national and club teams of both associations from UEFA competitions," Platini said in a UEFA statement.
"We must see a clear improvement, if not, we will not hesitate to take firm action.
"Violence in football is a core concern for us that needs to be addressed urgently. I have seen in my meetings with the heads of state of both Croatia and Serbia that they share our concerns and wishes to commit to finding solutions.
"We agreed on the need to build a strong plan of concrete measures which require strong leadership and commitment from both governments at all levels."