Ukraine’s interior minister says about 70 people have been arrested in an anti-terrorist operation in Kharkiv, one of three eastern cities where pro-Russian protesters have been occupying government buildings.
Police have reportedly retaken a building which had been seized by demonstrators.
Russia’s foreign ministry has warned Kyiv to stop military preparations in southeastern Ukraine that could lead to civil war.
Clashes between pro-Russian and pro-Ukrainian groups have continued, stoking fears of a new Crimea-like secession in the region.
In Donetsk, rebels occupying the regional government building declared a people’s republic and called for a referendum over leaving Ukraine on May 11.
With 40,000 Russian soldiers stationed on the borders of Ukraine, the US has called on Moscow to cease any destabilising tactics. US Secretary of John Kerry and Russia’s Foreign Minister Sergei Lavrov discussed the possibility of meeting for talks within the next 10 days, as relations between Washington and Moscow remain tense.