Ukraine's National Security and Defence Council has decided to launch a full-scale anti-terrorist operation involving armed forces to suppress pro-Russian demonstrators in the south-east of the country.
In a televised national address, Ukraine's interim president Oleksander Turchynov called on the protesters to vacate the government buildings and leave the region under an amnesty by today.
"We did everything to avoid human victims but we are ready to give an answer to all attempts at invasion, destabilisation and armed terrorist actions," Turchynov said.
"We will not allow Russia to repeat the Crimean scenario in the eastern regions of the country."
The move comes after a Ukrainian state security officer was killed and five others injured during clashes on Sunday between the military and pro-Russian separatists in the eastern city of Slaviansk.
The Ukrainian Special Forces had launched an armed confrontation in Slaviansk after activists armed with automatic weapons seized government buildings, and erected road blocks on the outskirts of the city, which is located about 150km from the Russian border.
Turchynov said the shooting of the officer is part of 'a war waged against Ukraine by the Russian Federation', to weaken and destroy the country.
Meanwhile, Russia's Foreign Ministry has branded the planned security operation as 'criminal', and called on the UN Security Council (UNSC) and the Organization for Security and Cooperation in Europe (OSCE) to urgently consider the crisis in Ukraine.
Moscow, which had denied its involvement in the current unrest, already warned Kiev against the use of force against Russian speakers, saying it 'would undermine the potential for cooperation', including talks scheduled to be held on Thursday between Russia, Ukraine, US and the European Union, the Guardian reports.
The UNSC reportedly held an urgent meeting yesterday to discuss the deepening crisis.