Ukraine crisis: over 20 killed in Mariupol as Putin marks victory in Crimea

^{Bullet holes and other damage following fierce fighting (GENYA SAVILOV/AFP)}

However, the medical authorities said that three people had been killed and 25 wounded.

Local people disputed the interior minister's version of events. They said the security forces also fired at unarmed civilians in the streets of Mariupol.

One man, who declined to be named, said that police officers had sided with the pro-Russian insurgents and helped them to take over the headquarters. 'Some of the police were on the side of the people,' he said. Uniformed police officers fought against interior ministry troops when the latter tried to seize back the building, added the witness.

Video footage, which has not been independently verified, showed civilians bringing armoured combat vehicles to a halt by standing in their path. At least one appears to have been captured by the crowd. Another vehicle made its escape only by firing its heavy machine gun over the heads of a cluster of people standing in its way.

^{Men carry away an injured firefighter (EVGENIY MALOLETKA/AP)}

Mariupol, the second-biggest city in Donetsk region with a population of 500,000, has become one of the most dangerous flashpoints in the confrontation between Ukraine's government and pro-Russian insurgents. The strength of feeling is such that other unverified video footage showed people kicking and spitting on a corpse, saying the dead man was a 'traitor' for siding with the government.

The rebels occupied Mariupol City Hall in the name of the 'Donetsk People's Republic' last month. Unlike elsewhere, the security forces in Mariupol appear to be making every effort to prevent pro-Russians from seizing any more buildings.

At least three people were killed outside a National Guard base in Mariupol last month when the troops opened fire with live rounds. On Wednesday, the security forces briefly recaptured City Hall after filling the building with tear gas. But they soon departed, allowing the pro-Russians to return.

^{Firefighters exit the wrecked building (MARKO DJURICA/REUTERS)}

Many people in Mariupol accuse the security forces of behaving in a heavy-handed way. The pro-Russian leaders of the 'People's Republic' will hold a referendum on independence for the region on Sunday. The security forces may also be trying to deny their enemies the ability to hold this poll in Mariupol.

Mr Avakov called on people to support the government and promised that 'terrorists' would be given no quarter. 'Those who have come with weapons, who seize buildings, who take people into captivity or torture them, the Ukrainian government will answer these people with one response: annihilation,' he said.

'Everybody chooses for himself. The situation has become black and white: the shades have been put aside. We have no choice, otherwise the country will become a burning buffer zone where death will become the norm and we will have to live on the ruins of the economy and the people's civil rights.'

Mr Avakov added: 'I address everybody: let's put aside feuds and interests: the country is at stake.'