Russian president greeted with patriotic fervour at second world war commemoration, while at least five are killed in southern city

Vladimir Putin made a triumphant first visit to Crimea on Friday, as the region held its first Victory Day commemorations since it was annexed by Russia two months ago. But the gravity of the crisis gripping the rest of Ukraine was underscored by more deadly clashes in the southern city of Mariupol.

Hospitals confirmed that at least five people had died and 40 had been wounded, according to Anna Neistat of Human Rights Watch, who had visited hospitals in the city. She said most had bullet wounds to the legs and chest from automatic weapons. In one hospital, six of the 15 casualties were policemen. Two dead bodies were visible on the street outside the police building, one of them of a policeman.

Ukraine's interior minister, Arsen Avakov, said on his Facebook page that 20 separatists had been killed and four captured, during an operation to free the police station from "terrorists".

A man jumps over a burning barricade outside Mariupol city hall. Photograph: Marko Djurica/Reuters

Locals in Mariupol had a different version, claiming the police had crossed to the side of the separatists, and both had been attacked by the army. However, with the chief of police supposedly taken hostage by the separatists, it seems likely that the police, like much of the city's population, had been split over whom to support.

Mariupol is one of at least a dozen cities in eastern Ukraine in which pro-Russian groups are agitating to follow Crimea's lead in seceding from Ukraine.

In Crimea, the Russian president spoke before an adoring crowd about the "return to the motherland" of a region that was once part of Russia. Putin later said other countries should "show regard for our legal interests, including the restoration of historical justice and the right to self-determination".

The patriotism reached fever pitch in Sevastopol before his arrival as Russian fighting vehicles, Putin's favourite biker gang and militiamen who helped Crimea break away from Ukraine paraded through the city.

Tens of thousands chanted "Russia!", "Victory!" and "Thank you!" as 1,000 troops, 60 military vehicles, thousands of veterans and other groups passed by over two hours.

Putin watched an air and naval show featuring 70 aircraft to symbolise the 70th anniversary of Sevastopol's liberation from the Nazis by Soviet forces, which lost more than 200,000 in fighting.

Pro-Russia militiants take part in a Victory Day rally in the eastern Ukrainian city of Donetsk. Photograph: Alexander Khudoteply/AFP/Getty Images

"We're all happy to be part of Russia. Hooray for veterans!" shouted seven-year-old Mikhail Rybak, as onlookers cheered him.

A reported 97% of voters chose to join Russia in a referendum in Crimea in March which did not include an option to retain the status quo. The vote was boycotted by most Crimean Tatars, who make up about 15% of the peninsula's population.

A referendum is also planned in east Ukraine on Sunday , which will ask residents if they wish to create a "Donetsk People's Republic". Putin said on Wednesday that the separatists should postpone their referendum, but they refused. The separatist movement is divided between those who want to join Russia and those who merely want more autonomy within Ukraine, but opinions are becoming more polarised as the military operations continue in the east of the country.

In Mariupol, there was a mood of rage after the Ukrainian army left, intensified by the fact that many people were intoxicated from the earlier Victory Day celebrations. Several fights broke out in the crowd, but the main anger was reserved for Kiev.

"We will never live with these filthy fascists again. . Ukraine as a country is over," said Vladimir, 27. "Imagine coming here on Victory Day and doing this."

At Café Arbat, where pools of blood were visible on the ground, one of the waitresses, Lena, said that three unarmed men had been shot by Ukrainian soldiers.

"I wasn't for one side or the other until today, but after seeing this, I have the feeling I want to take up a weapon myself and kill these people," she said.

"I'm 50 years old and they made me fall on the ground and hide from bullets, in my own cafe, in my own town."

The separatists also seized an armoured personnel carrier that had been abandoned by the Ukrainian army due to engine problems, and towed it through the city, waving the flag of the self-proclaimed Donetsk People's Republic from the top.

Earlier in the day, several thousand people gathered in Donetsk's Lenin Square for the victory celebrations. The mood was heavily influenced by the current situation, with several speakers comparing the victory over the Nazis to the "fascist junta" in Kiev.

The few living second world war veterans on the stage were joined by fighters from the self-proclaimed People's Republic of Donetsk, many of whom were armed with Kalashnikovs, sniper rifles or, in one case, a giant mallet.

Officials said on Friday that the referendum planned for Sunday was not about independence or joining Russia, but merely about giving the region more autonomy.

However, speeches from the stage were unequivocal.

"We are Russians, and Russia is our homeland," said Denis Pushilin, the de facto head of the separatist movement. "Russians here are not occupiers. They are our brothers."

Victory Day celebrations in Kiev took place amid tight security, with police reinforced by pro-Ukrainian self-defence groups. The cancellation of a traditional military parade meant festivities were more modest than usual.

Many locals were wearing red poppies rather than the black and orange St George ribbon representing the Soviet Union's victory in the second world war that has been widely worn by anti-Kiev insurgents.

"The St George ribbon is associated with events in the east where they are killing people … traitors wear the St George ribbon," said Galina Prikhodko, 26, who had come to lay flowers near the city's Motherland statue.

As night fell in Mariupol, local separatists rebuilt barricades in the centre of the city and returned to the local administration building, now half gutted by fire, which has been captured and abandoned twice now by Ukrainian forces in the past week. Many expected the army to return overnight. Videos from earlier in the day appeared to show Ukrainian soldiers firing on unarmed protesters, while others showed protesters in the crowd with weapons returning fire.

Among the crowds, however, there was no doubt who was to blame. A large group of men set upon a lone dissenter who said he thought the region and Kiev should live in peace, and he had a beer bottled smashed on his head before fleeing the square.

"This is awful of course, all this drinking, and low-cultured behaviour," said Nina Tuvayeva, a pensioner looking on. "I'm against all of this, and I wanted a united Ukraine, a country that would be like Switzerland or Belgium, but they don't want that, so now our only hope is Russia. Ukraine is over."