Activists break into buidlings in Donetsk, Odessa and Luhansk as poll finds many in those areas would like reunification

Pro-Russian forces in the eastern Ukrainian city of Donetsk have overrun a government building and proclaimed they have taken over the regional administration, locals have told the Guardian. In an ominous sign of the spread of anti-Ukrainian sentiment among Russian-majority parts of the country, similar actions were reported in Odessa on the Black Sea and Luhansk, near the border with Russia.

At about midday on Monday100 people broke into the Donetsk regional administration building via the back door, secured the ground floor and meeting room of the administration office, and hoisted a Russian flag atop the building. Several hundred people were also waving Russian flags and shouting slogans in a nearby square.

"The separatists announced the creation of their own regional administration headed by Pavel Hubarev," Oleksiy Matsuka, editor of the Novosti Donbassa local newspaper, told the Guardian. "Their authority isn't recognized by anybody." He added that the local police had launched a criminal investigation into the incident.

The attack may have been prompted by the appointment by the new authorities in Kiev of a new governor for the region, oligarch Sergiy Taruta.

There were similar scenes in Luhansk overnight after 400 people broke into the local administration waving Russian flags and the flags of Russkoye Edinstvo pro-Russian block. The invaders claimed they did not recognise Kiev's authority and called on Putin to bring Russian troops to Ukraine.

A further 3,000 pro-Russians rallied outside the regional administration in Odessa, chanting "referendum". Later they faced off against Ukrainian nationalists who demanded they remove the Russian flag. The police separated the two groups and the governor of the Odessa region, Mykola Syrotiok, started negotiations with representatives of both sides behind closed doors.

The residents of Donetsk, Luhansk and Odessa, together with Crimea, have the highest pro-Russian aspirations of any of the Ukrainian regions. A poll by the Democratic Initiatives Foundation and the Kiev International Institute of Sociology presented on Monday found that when asked if they wanted Ukraine to reunify with Russia, 33% from Donetsk approved, as did 24% in Luhansk and Odessa and 41% in Crimea.

"But in Ukraine as a whole, the number of people who would like to have one state with Russia is no more than 13%," said Volodymyr Paniotto, head of the Kiev International Institute of Sociology. He added that only 16% of Russians wanted unification.

"I don't think Russia aims with its current aggression to annex Ukraine east and south, or even Crimea – they don't need it," said Valery Chaly, deputy head of the Razumkov thinktank. "Russia only wants to keep Ukraine on a lead … Putin wishes to prevent the final decay of Soviet Union."