Crimean leader Sergei Aksyonov tweets that if Kyiv launches a military operation, "without the right," then "the courteous" would be legally justified in entering Ukrainian territory.

Speaking in a live televised address, Ukraine's acting President Oleksandr Turchynov accused Russia of waging "war" against Ukraine, announced plans to launch a "large-scale counterterrorist operation" involving the Ukrainian military.

As reported earlier, pro-Russian protesters took over city of Slovyansk on April 12 and targeted several other municipalities in eastern Ukraine.

Activists also took over government buildings and police stations in cities of Western Ukraine, demanding a referendum on autonomy and possibly joining Russia.

Meanwhile Turchynov promised amnesty for pro-Russian separatists who lay down their arms by the morning of April 14.