The family of Oleg Sentsov, the Ukrainian film director imprisoned in Russia who is on hunger strike, have called on President Vladimir Putin to release him before the World Cup, which kicks off on Thursday.
Sentsov has been on hunger strike since 14 May, saying he will stop only if all Ukrainian political prisoners are released.
On Saturday, Putin spoke by phone with his Ukrainian counterpart, Petro Poroshenko, raising hopes that a last-minute deal could still be done before the World Cup.
Putin appeared to pour cold water on any suggestion of a swap during a televised phone-in session on Thursday.