The declaration and subsequent appeal for Russian military help have faced the Kiev's new pro-Western leaders with new danger of disintegration and urged the Ukrainian government to put more pressure on Western powers to act.
The ex-Soviet nation on the EU's eastern frontier continues to be watched by tens of thousands of Russian troops who had already annexed the Black Sea peninsula of Crimea in response to last month's ouster in Kiev of a Moscow-backed government.
Several heavily Russified eastern regions now want to stage referendums on joining Russia when Ukraine holds snap presidential polls on May 25 that feature two frontrunners who both want to tie the vast country's future to Europe and break its historic dependence on its eastern neighbor.
The political pressure on Kiev's embattled leaders reached boiling point on Sunday when thousands of activists chanting "Russia!" seized administration buildings in Kharkiv and Donetsk as well as the security service headquarters in the eastern region of Lugansk.
The Donetsk activists went one step further on Monday by proclaiming the creation of a sovereign "people's republic" in the region of about five million people.
Footage posted on YouTube showed one bearded Russian speaker telling the packed assembly from a podium: "Seeking to create a popular, legitimate, sovereign state, I proclaim the creation of the sovereign state of the People's Republic of Donetsk."
The industrial eastern region's Ostrov (Island) news website reported that the activists later resolved to join the Russian Federation in a move similar to the one taken by Ukraine's Crimea peninsula last month.
The news site said the resolution was met with a huge roar and chants of: "(Russian President Vladimir) Putin, help!"
The Interfax news agency reported that the self-proclaimed leaders had also vowed to hold a regional sovereignty referendum no later than May 11.
More footage aired on Ukraine's Channel 5 television showed an unidentified speaker asking Putin to send a "peacekeeping contingent of the Russian army" to Donetsk to help the region stand up to Kiev's rule.
Ukraine's latest bout of political turmoil prompted Prime Minister Arseniy Yatsenyuk to send his deputy Vitaliy Yarema to the region in order to establish a semblance of control.
The Donetsk administration building on Monday was surrounded by about 2,000 Russian supporters -- some of them armed.
NJF/NJF