Pro-Russian protesters seized state buildings in three east Ukrainian cities, triggering accusations from the pro-European government in Kiev that President Vladimir Putin was orchestrating "separatist disorder".
The protesters stormed regional government buildings in the industrial hub of Donetsk.
Also security service offices in nearby Luhansk were raided with people waving Russian flags demanding a Crimea-style referendum on joining Russia.
Protesters also later seized the regional administrative building in Kharkiv, Ukraine's second largest city.
All three cities lie close to Ukraine's border with Russia.
Interior Minister Arsen Avakov vowed to restore order in eastern Ukraine.
He said it would be done without using violence.
Mr Avakov also accused Ukraine's ousted president Viktor Yanukovych, whose political base was in Donetsk, of conspiring with Mr Putin to fuel tensions.
"Putin and Yanukovych ordered and paid for the latest wave of separatist disorder in the east of the country.
The people who have gathered are not many but they are very aggressive," Mr Avakov said in a statement on his Facebook page.
"The situation will come back under control withoutbloodshed. That is the order to law enforcement officers, it's true.
But the truth is that no one will peacefully tolerate the lawlessness of provocateurs."
Acting President Oleksander Turchynov called an emergency meeting of security chiefs in Kiev and took personal control of the situation, the parliamentary press service said.
Mainly Russian-speaking eastern Ukraine has seen a sharp rise in tensions since Mr Yanukovych's overthrow in February and the advent of an interim government in Kiev that backs closer ties with the European Union.
Russia has branded the new government illegitimate and has annexed Ukraine's Crimea region.
It has cited threats to its Russian-speaking majority - a move that has sparked the biggest stand off between Moscow and the West since the end of the Cold War.