Ukraine has put off a planned summit of eastern European leaders after a number of them declined to attend in protest over the treatment of jailed opposition leader Yulia Tymoshenko.
"Due to the inability of some European state leaders to take part in the summit ... Ukraine considers it sensible to delay the summit and not to hold it in the city of Yalta on May 11-12," the foreign ministry said.
The ministry said it would announce new dates later.
In a move that could foreshadow similar action during the Euro 2012 football championship, which Ukraine co-hosts with Poland next month, at least eight European presidents have refused to attend the planned summit.
Most of them have said this was due to the treatment of Ms Tymoshenko, a former prime minister and a critic of Ukrainian President Viktor Yanukovich.
She was sentenced to seven years in prison last October for alleged abuse of office, which she denied. The European Union says her conviction was politically motivated.
Some of those who had planned to attend the summit, among them Polish President Bronislaw Komorowski, said they had intended to raise Ms Tymoshenko's case with Mr Yanukovich.