Pro-Russian separatists on Wednesday declared a republic in Odessa, a region in southern Ukraine on the Black Sea, following the lead of separatists in the eastern region of Donetsk, the epicenter of the uprising against authorities in Kiev.

"As of today, the region of Odessa is declaring itself the people's republic of Odessa, where all the power belongs to just the people living in its territory," the pro-Russian separatists said in a statement posted on their Web site.

A civil war has broken out in Ukraine and residents should block roads and underground passageways in the city of Odessa starting at 4:00 p.m. on Thursday, the separatists said.

"If you do not want a war that turns our country into ruins, like Syria and Libya, that costs thousands of lives, then you have to act. Odessa is already surrounded by enemy checkpoints. A state of war has already been declared in the country," the pro-Russian separatists said.

The call for open rebellion is aimed at keeping Ukrainian army troops from entering Odessa and getting residents to join the liberation movement in the south, where ethnic Russians are demanding a region-by-region political status referendum.

Pro-Russian separatists declared a people's republic in the Donetsk region, where they have seized government buildings in several cities, on April 7.

Ukraine's acting president, Oleksandr Turchynov, issued an ultimatum on Sunday to the separatists, ordering them to lay down their arms and leave occupied government buildings in the southeastern region of the country by 9:00 a.m. on Monday.

Turchynov said Sunday that he would use the army to restore order and signed a decree guaranteeing that those complying with the ultimatum would not be prosecuted as long as they did not injure anyone.

Russia labeled Turchynov's decision to use the army to end the protests a "criminal" action to crush "peaceful demonstrations." EFE