Ukrainian troops were not battling only pro-Russian separatists on the east but also the same special forces, which Russia sent to Crimea before its annexation in March, UK Foreign Secretary William Hague has reported.

"It is clear that the leading elements of these forces [in southeastern Ukraine], from their training, their equipment, their identical behavior to the infiltrators in Crimea, are not simply pro-Russia forces, they have been Russia forces," he said at a press conference in Kyiv on Wednesday.

According to Hague, the individuals that seize the buildings in the southeast are hired criminals, which aren't the representatives of the local population.

Russia's aim is to prevent Ukraine's presidential poll at all cost, he said.

Hague also accused Russia of trying to "orchestrate conflict" in Ukraine ahead of the May 25 presidential election.

"Russia has illegally annexed part of Ukraine's territory and is actively creating unrest in other parts of the country," Hague said. "I think they want to stop you [Ukraine's citizens] from holding the elections. That is the objective, and that reflects a fear of the power of democracy."

The UK foreign secretary said that there are no doubts that the presidential elections in Ukraine would be held in the complicated atmosphere.

"They [Ukrainians] cannot be bullied out of having their elections by disorder that is deliberately fomented and coordinated from another country – in this case from Russia. They are entitled to have their democratic choice, to choose their own president," he said.