President Viktor Yanukovych has accused Yulia Tymoshenko, his jailed rival, of involvement in a contract killing 16 years ago. His comments suggest he is unmoved by a boycott of Euro 2012 football matches by Western governments.
Ms Tymoshenko, who is serving a seven-year sentence for alleged abuse of office when Prime Minister, has dismissed any link with the killing of Yevhen Shcherban, a businessman, as "absurd". Her supporters accused the President of acting like a dictator.
The prosecution and conviction of Ms Tymoshenko has led to a boycott of Euro 2012 matches in Ukraine by some European politicians, who say her trial was politically motivated.
Ukraine is hosting the European Football Championship with Poland and will stage the final in the capital, Kiev, on 1 July.
Mr Yanukovych's tough words linking Ms Tymoshenko to the killing of Shcherban in 1996, suggested that he was ready to ride out the diplomatic protests and would not bow to pressure to release her.