Pro-Russia demonstrators have begun fortifying the entrance to the Donetsk regional administration building, which they occupied on Monday in a declaration of independence from the pro-European government in Kiev.

Popular Soviet songs blared from loudspeakers positioned outside the building on Tuesday, where hundreds of people – some waving Russian flags – gathered in support of the protest, occasionally chanting "Russia!".

Protesters appeared to be digging in for a siege. Long lines were formed to pass ripped-up paving stones to the building's entrance, firming up barricades of tyres and barbed wire. Young men moved about the ransacked eight-storey building, many wearing masks and holding clubs.

Earlier in Kharkiv, Ukranian police detained 70 pro-Russia demonstrators who had occupied a regional government building there. The interior minister, Arsen Avakov, said the Kharkiv protest site had been cleared in an 18-minute "anti-terrorist" operation.

Arakov pinned responsibility for the building's occupation on the Russian president, Vladimir Putin, and Ukraine's ousted Moscow-backed president Viktor Yanukovich. "All this [in Kharkiv] was inspired and financed by the Putin-Yanukovich group," Avakov said.

Police stand guard in front of the Kharkiv regional state administration building. Photograph: Anatoliy Stepanov/AFP/Getty Images

The Donetsk demonstrators appear determined not to be removed so quickly. The protest leadership has declared a new temporary government and vowed to hold a referendum on the Donetsk region's status by 11 May. According to Deniz Pushilin, a representative of the new "people's council" of Donetsk, around 800 protesters occupied the building overnight.

Alexander, an unemployed Donetsk resident, said he supported the protesters' takeover and the idea of a federalised restructuring of Ukraine that would allow for greater regional autonomy. "Let the people decide in the referendum," he told the Guardian.

In Kiev, frayed nerves erupted in an exchange of blows in the Ukrainian parliament chamber when the communist leader Petro Symonenko accused nationalists of playing into the hands of Russia in its extreme response to anti-government protests.

Two deputies from the far-right nationalist Svoboda party took exception to Symonenko's charges and seized him while he was speaking at the rostrum. His supporters rallied to his defence and a brawl broke out with deputies from other parties joining in and trading punches.

Deputies brawl in parliament in Kiev. Photograph: Maksim Marusenko/EPA

The Donetsk protesters based their call for independence from Kiev on charges that the post-Yanukovych government was serving western interests and ruining the economy. "Now the economic problems are only starting, and more people will come here," Alexander said. "They need to put their energy towards something. That's why I'm for federalisation and a referendum."

Others accused the "junta" in Kiev of representing only western Ukraine and infringing on Russian speakers' rights. "If we have to choose between the EU and Russia, then Donetsk is with Russia," said Marina Magdalena, a jurist who had brought her young daughter out in support of the protest. "If they don't let us live autonomously in Ukraine, then we should join Russia."

"This prostitute Tymoshenko, let her stay out of Donetsk," Magdalena shouted for the benefit of fellow protesters, referring to a visit on Monday by the former prime minister Yulia Tymoshenko, who will be running in next month's presidential elections. Her comment drew cheers of support.

Petro Poroshenko, a Ukrainian oligarch and pro-Europe presidential candidate who is leading the polls, was no more popular with the Donetsk demonstrators. Responding to a prompt from her mother, Magdalena's young daughter shouted for the benefit of video cameras: "Poroshenko go to hell!"