Kiev: Ukraine`s Western-backed leaders pushed troops and tanks toward a flashpoint eastern city on Tuesday to quash a separatist insurgency that has been backed by Russia.
Here is a chronology of the main developments in the heavily Russified east of Ukraine over the past 10 days:
SUNDAY, April 6: Pro-Russian demonstrators overwhelm police to seize local government buildings in the million-strong city of Donetsk and demand a referendum on turning the region into part of Russia, as happened in Crimea last month.
In Lugansk, pro-Russian protesters occupy a building belonging to Ukraine`s SBU security services.
In Kharkiv, the main eastern city, clashes erupt between more than 2,000 pro-Russian protesters who take over the offices of the regional governor and nationalists loyal to Kiev.
MONDAY, April 7: Pro-Russians occupying the offices in Kharkiv are forced out of the building.
But those occupying government offices in Donetsk declare an independent republic and also take over the SBU security service office.
Ukraine`s government accuses Russia of wanting to invade the country and break it up. Washington calls on Russian President Vladimir Putin to cease "destabilising" Ukraine.
TUESDAY, April 8: In a day of clashes in Kharkiv, Ukrainian security officials arrest 70 pro-Russian militants throwing petrol bombs at the local government building.
One of the pro-Russian leaders in Donetsk declares an interim local government.
WEDNESDAY, April 9: Pro-Russian militants in Lugansk occupying the SBU building dig in, despite the rising risk of an assault to dislodge them.
SATURDAY, April 12: Pro-Russian gunmen wearing camouflage uniforms and balaclavas take over the police station and the security services building in the town of Slavyansk, 60 kilometres (40 miles) from Donetsk.
In Donetsk, pro-Russian militants take over the police headquarters without encountering resistance.
In Kramatorsk (70 kilometres, 45 miles north of Donetsk), masked and uniformed gunmen armed with Kalashnikovs attack the police and municipal headquarters.
SUNDAY, April 13: Ukrainian special forces launch an unsuccessful assault to try to dislodge the pro-Russian gunmen from Slavyansk. One Ukrainian special forces officer is killed in the firefight and five are wounded.
MONDAY, April 14: Kalashnikov-wielding militants in Slavyansk take command of its administration building before asking Putin to send in his troops.
In the Donetsk region town of Gorlivka, pro-Russians attack a police station with men in gas masks, pelting the building with Molotov cocktails before smashing its windows with rocks and bats.
US and Russian Presidents Barack Obama and Putin confront one another in telephone talks.
TUESDAY, April 15: Ukraine sends a large armoured column and special forces toward Slavyansk in the Western-backed team`s most forceful response to date to raids in the east.
A Ukrainian general leading the push warns that gunmen who do not lay down their arms will be "destroyed".
Russian Prime Minister Dmitry Medvedev declares that "Ukraine is on the brink of civil war".
Putin calls for the United Nations to condemn Kiev`s actions, while the White House describes the military operation as "measured".
