Ukraine’s Interior Ministry has launched an anti-terrorist operation in the eastern city of Kharkiv by blocking the city center, said acting Interior Minister Arsen Avakov. At least 70 activists have been arrested by the police.

“The anti-terrorist operation has begun. The center of the city and Metro stations are closed. As soon as we finish the operation, we will unblock them,” wrote Avakov on his Facebook page.

Pro-Russian protesters seized government buildings in the eastern cities of Kharkiv, Luhansk, and Donetsk on April 6, demanding that referendums be held on whether to join Russia.