Belarussian President Alexander Lukashenko, a target of European Union sanctions over human rights, shared a VIP box with European leaders at the Euro 2012 final on Monday.
Pictures published by private Ukrainian news agency UNIAN showed Lukashenko and his son Nikolai, aged seven, sitting next to Georgian leader Mikheil Saakashvili and other ex-Soviet leaders at the Olympic stadium in Kiev.
Brussels has introduced travel bans and asset freezes against Lukashenko and a number of his officials after his government cracked down on opposition last year in the aftermath of his re-election as president.
It was not clear, however, if he had met or shaken hands with the prime ministers of Spain and Italy who sat in the same box, but to the other side of Ukrainian President Viktor Yanukovich and other local officials.
Yanukovich himself has been the target of a diplomatic boycott by other European leaders throughout the Ukrainian half of a championship it has co-hosted with Poland.
The EU has criticised as selective justice a ruling by a Ukrainian court last October which sentenced Yanukovich's opponent, former prime minister Yulia Tymoshenko, to seven years in prison on abuse-of-office charges.
But both Spanish and Italian leaders put the boycott announced by a number of European governments aside when their teams made it to the final.