Armed men have seized a police department in the eastern Ukrainian city of Slaviansk, Interior Minister Arsen Avakov said Saturday as he promised a tough response, according to dpa. The men were dressed in camouflage uniforms when they stormed the building in Slaviansk, which is about 100 kilometres north of the regional capital Donetsk. On Friday, pro-Russian separatists in Donetsk declared an independent 'Peoples' Republic' inside the barricaded regional administration building. The protesters said they would defend themselves with bricks and Molotov cocktails against any attempts to evict them. Acting Ukrainian premier Arseniy Yatsenyuk traveled to Donetsk on Friday and offered the protesters concessions. Yatsenyuk said that local administrations should no longer be appointed by Kiev and that referendums at the regional level should be allowed. He met regional officials, but did not speak to any of the protesters. Under the current constitution, local governors and their administrations are appointed by the Ukrainian president and only national referendums are allowed. Yatsenyuk did not say if it would be possible to conduct regional referendums without the consent of the government. Kiev has condemned as illegal a referendum in Crimea last month, which resulted in the Black Sea peninsula's accession to Russia. EU foreign policy chief Catherine Ashton has announced plans for a meeting in Brussels on April 17 among the European Union, United States, Russia and Ukraine, as part of 'diplomatic efforts to de-escalate the crisis in Ukraine and to find a political solution.' The government in Kiev and Western nations accuse Russia of destabilizing Ukraine and instigating separatism in the country's eastern Russian-speaking regions.