A timeline of the main developments in the armed separatist uprising in eastern Ukraine, after Russia's annexation of the Crimean peninsula in March.

The unrest started in the east and south of the former Soviet republic after pro-European protesters forced the Kremlin-backed government in Kiev from power on 22 February.

6 April: Tensions soar when pro-Russian demonstrators seize local government buildings in several towns in eastern Ukraine, including Donetsk, Kharkiv and Lugansk.

7 April: Pro-Russians occupying offices in Donetsk declare an "independent republic". Ukraine's government accuses Russia of wanting to invade the country and break it up.

12 April: Pro-Russian militants launch offensives in the towns of Slaviansk and Kramatorsk, to the north of Donetsk, where they take over the police headquarters.

13 April: Kiev announces an "anti-terrorist" operation in the east.

16 April: Ukrainian troops turn back from Slaviansk, after pro-Russians seize six armoured vehicles. Militants seize Donetsk town hall.

17 April: A deal is reached in Geneva between Ukraine, Russia, the United States and the European Union to "de-escalate" tensions.

18 April: The Kremlin confirms Russia has built up its military presence on the border. NATO puts the deployment at 40,000 troops.

20 April: The leader of pro-Russian demonstrators in Slaviansk appeals to Moscow to send in peacekeeping troops after a deadly shootout.

21 April: In Lugansk, protesters pledge to hold their own local referendum on autonomy on 11 May.

22 April: In Kiev, US Vice President Joe Biden says Russia faces "isolation". Washington orders 600 soldiers to Poland and the ex-Soviet Baltic states.

23 April: Russia says it will respond if its interests are attacked in Ukraine.

24 April: Ukraine's military launches assault on Slaviansk. Up to five rebels are killed, according to Kiev. Russian President Vladimir Putin describes it as a crime that will "have consequences".

25 April: Ukrainian Prime Minister Arseny Yatsenyuk accuses Moscow of seeking to trigger a "third world war". A group of OSCE military observers are detained in Slaviansk.

26 April: Mr Yatsenyuk cuts short a Vatican trip to see Pope Francis, saying Russian warplanes violated Ukraine's airspace seven times overnight. Russia denies the claim.

27 April: Rebels say the OSCE observers are "prisoners of war" and present them in front of the press, where they say they have not been mistreated.

28 April: West imposes new sanctions on Moscow. Russia vows a "painful" response. Russia says troops have returned to barracks after conducting exercises on the border with Ukraine. The West says there is no sign of this pull-back. Russia assures the US it will not invade Ukraine.

29 April: Russia warns sanctions could harm Western interests in Russia's lucrative energy sector, denies there are Russian forces in eastern Ukraine.

30 April: Kiev says its armed forces are on "full combat alert" against a possible Russian invasion. Interim president Oleksander Turchynov admits Kiev is "helpless" to prevent rebels over-running towns. The International Monetary Fund approves $17bn aid deal for the beleaguered Ukrainian economy.

1 May: About 300 pro-Russian militants seize the prosecutor's office in Donetsk amid violent clashes with police. Conscription reintroduced for all Ukrainian men aged 18-25.

2 May: The bloodiest day since new government came to power. At least nine die in fresh army assault on Slaviansk. In the southern port city of Odessa, dozens die after clashes between pro-Russian militants and supporters of national unity ends in a massive blaze.

Russia declares the Geneva peace plan dead and calls an emergency UN Security Council meeting. US President Barack Obama says he will step up sanctions if Moscow destabilises Ukraine before planned 25 May elections.

3 May: Rebels in Slaviansk release the seven OSCE inspectors after intervention by a Kremlin envoy.