Kiev - The crisis in Ukraine began in November last year as a protest against the government dropping plans for closer economic ties with Europe.
But it has since snowballed into the biggest stand-off between the West and Russia after Moscow annexed Ukraine's Crimean peninsula and the port city of Sevastopol in February, following the ouster of Ukrainian president Viktor Yanukovich.
Russia's refusal to remove its troops from Crimea or renounce its support for pro-Russian separatists in Ukraine have presented a serious challenge to global principles about sovereignty.
Moscow further raised tension in eastern Europe by massing tens of thousands of troops in the regions bordering eastern Ukraine.
Fighting in various parts of Ukraine has continued unabated since April between government forces and the separatists who want a union with Russia. The rebels have seized government buildings and proclaimed at least two "people's republics" in separate provinces.
The new Ukrainian government under President Petro Poroshenko, who was elected in May, has vowed a hard line against the separatist insurgency, resulting in more intense fighting in eastern areas like Donetsk, a rebel stronghold.
Nato secretary-general Anders Fogh Rasmussen has called the crisis between Ukraine and Russia the greatest threat to European security since the end of the Cold War.
The United States has slapped sanctions on Russia to punish it for its aggression in Ukraine, and sent military assets and troops to the region in a show of force.
But US President Barack Obama has ruled out military action in Ukraine, with Moscow showing little interest in compromising.
Some commentators, however, say the downing of Flight MH17 over eastern Ukraine could prove a turning point for the political stalemate by prompting global leaders to take tougher action to end the fighting.
The Malaysia Airlines jetliner was brought down near the village of Grabove, about 40km from the border with Russia and near Donetsk, which has seen fierce fighting in recent months.
"This outrageous event underscores that it is time for peace and security to be restored in Ukraine," said Mr Obama, adding that Russia had to do more to quell the rebel violence.
He and several world leaders, including German Chancellor Angela Merkel, have called for an immediate ceasefire so investigators could reach the crash site.
"Moscow may have a last chance now to show that it really is seriously interested in a solution," Germany Foreign Minister Frank-Walter Steinmeier told Bild am Sonntag newspaper.
"Now is the moment for everyone to stop and think to themselves what might happen if we don't stop the escalation."
Stop and think "Moscow may have a last chance now to show that it really is seriously interested in a solution. Now is the moment for everyone to stop and think to themselves what might happen if we don't stop the escalation." - German Foreign Minister Frank-Walter Steinmeier
Months of upheaval
Nov 21, 2013:
Protests break out after the Cabinet of then Ukrainian President Viktor Yanukovych abandons an agreement to form closer ties with the European Union.
Feb 22, 2014:
Mr Yanukovych flees Kiev as thousands of protesters take control of government offices and houses in the capital.
Days later, pro-Russian gunmen seize key buildings in the strategic Crimean peninsula.
March 16, 2014: Crimea,
effectively under Moscow's influence by now, votes in a referendum to rejoin Russia.
April 6, 2014: Pro-Russian
protesters take over government buildings in eastern Ukraine, pushing for a Crimea-style referendum. Bloody clashes with government forces ensue.
April 7, 2014: Militants seize
government armouries and arm themselves with automatic weapons. Some declare their regions "people's republics" independent of Ukraine.
Fighting breaks out between militants and Ukranian troops.
April 17, 2014: Russia,
Ukraine, the United States and the European Union meet to end the crisis in Ukraine. But lingering suspicion hamper efforts for a truce.
May 25, 2014: Voters pick
Mr Petro Poroshenko as the new President of Ukraine. He vows a hard line against the separatist insurgency and rules out negotiating with them, resulting in more intense fighting.
July 17, 2014: Malaysia
Airlines Flight MH17 crashes near Hrabove in Donetsk, killing all 298 people on board.
The United States says the plane was shot down with a missile, fired from an area controlled by pro-Russian separatists
Key players in the conflict
The Russian President has been calling for a ceasefire in eastern Ukraine for at least two months. But there is widespread suspicion in the West that Russia has been re-arming the separatists with the aim of splitting up its neighbour. At the start of the Ukraine crisis, Mr Putin emphasised that he did not want to see a "divided Ukraine", but also said he would not tolerate instability in the country and discrimination against ethnic Russian citizens.
But some analysts believe Mr Putin entertains a long-term strategic aim: keeping Ukraine at least partly in Russia's orbit and preventing it from joining Nato.
Others believe he has to face down nationalists at home who are pressuring him to send in troops to support the rebels.
The varied speculation might explain his determination to annex the Crimea peninsula, a strategic territory with many ethnic Russians, but unwillingness to openly support separatists in east Ukraine.
Early this month, newly elected Ukraine President Petro Poroshenko showed readiness to talk to the rebels in the hope of ending the hostilities, following increasingly brutal fighting.
Such a talk might bring about a deal favourable to Russia.
It remains to be seen whether the downing of Malaysia Airline's Flight MH17 will hamper or help further Mr Putin's plan.
United States President Barack Obama has steadfastly called for a de-escalation of the situation in Ukraine since trouble broke out in the country. He has also repeatedly warned Moscow that it will face further isolation and ever-deeper sanctions if it does not refrain from meddling in the crisis and enable Kiev to restore national stability.
Last month, the President announced a fund of up to US$1 billion (S$1.24 billion) which, among other things, will help Georgia, Moldova and Ukraine develop the capacity to partner the United States and Nato.
However, analysts read his response to the crisis as a reactive policy marked by tough but hollow rhetoric.
As in the case of Syria, Mr Obama has again shown himself to be risk-averse, apparently worried that the cost of an open intervention in Ukraine would be too high.
But Mr Obama was quick to put the onus on Russia to end the crisis following the MH17 incident, pointing out that "violence and conflict inevitably lead to unforeseen consequences".
While the world is appalled by the tragedy, Mr Obama reminded the Russians and the separatists that they have the capacity to end the fighting.
It remains to be seen whether they will heed the growing international pressure headed by Mr Obama.
When he was elected President of Ukraine on May 25, Mr Poroshenko said he would take a hard line on the separatists, swearing that "talking to gangsters and killers is not our path".
Since then, he has stepped up the fight against the separatists, but also showed flexibility when he sought a ceasefire as the war came to a stalemate.
He has said the crisis can be resolved only with the help of Russia.
Mr Poroshenko, a minister in previous governments, has implemented some democratic reforms, including decentralisation in Ukraine, and adopted pro-West policies, since taking office.
He called the downing of MH17 an act of "terrorism" and has denied that his men launched the missile.
The rebel politician and self-proclaimed prime minister of the "Donetsk People's Republic" was appointed to the post by its Supreme Council on May 16 this year.
A Russian citizen, Mr Borodai earlier worked as a political adviser to Mr Sergey Aksyonov, the Governor of the Republic of Crimea.
Igor Ivanovich Strelkov
The rebel commander heads the Donbass People's Militia paramilitary group, which is an armed pro-Russian militant group which declared allegiance to the self-proclaimed Donetsk People's Republic.
Strelkov was charged by the Ukraine authorities with terrorism and has been sanctioned by the European Union for his leading role in the insurgency in eastern Ukraine.
He admitted that he served in the Russian Federal Security Service until March last year. According to Ukrainian authorities, he is a retired Russian military intelligence officer who participated in the Crimea crisis.
He has also expressed hard-line views on eliminating enemies of the Russian state.
This article was first published on July 20, 2014.
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