Russia wants Ukrainian nationalists punished for their part in clashes that marred World War Two commemorations.
On Monday, violence broke out as Ukrainian protesters attempted to disrupt the May 9 celebration of the Russian victory over the Nazis.
The sickle and hammer flag was burnt and a wreath dedicated to the Soviet Red Army was destroyed.
The violence took place in the western Ukrainian city of Lviv, which has a troubled history with Russia. The city was occupied by Soviet troops in 1939, and some welcomed the Nazis as liberators when they arrived two years later. Around 50 nationalists fought with riot police and one of the demonstrators was shot in the leg.
Nationalist supporter Oleksander Pozniakov claimed his group did not initiate the trouble, saying:
“Communists came here and provoked us by bringing the red flag. This is a day to respect veterans. It shouldn’t be exploited by political parties.”
Fighting between Ukrainian nationalists and pro-Russian demonstrators also prevented people reaching a monument in Lviv honouring the Red Army. Unable to get close enough, some threw flowers. One Russian supporter said she wanted to celebrate the history of Europe and Ukraine being liberated from the fascist Nazis.
The May 9 celebration often causes tension between the two sides in a country divided over its relationship with Russia.