The Ukrainian military claims Malaysia Airlines Flight 17 was shot down by a Russian missile, although exactly what brought down the plane in rebel-held eastern Ukraine has not been confirmed.
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Here's a refresher about what's going on between Ukraine and Russia.
1. What sparked the current conflict between Ukraine and Russia?
The conflict dates back to before the dissolution of the Soviet Union. Tensions between Ukraine and Russia escalated this past February, when protests for closer Ukrainian ties to the European Union drove out Ukraine's pro-Russian president, Viktor Yanukovych. Back in November 2013, Yanukovych refused to sign an agreement with the EU that contributed to the political turmoil.
2. How badly has the violence escalated?
Fighting between pro-Russia rebels and Ukrainian troops has killed more than 400 people in eastern Ukraine in the last few months, the U.N reported, while tens of thousands have fled their homes.
The Malaysia Airlines flight is the third tragic air accident in the territory after an An-26 military transport plane was shot down on July 14 and a Ukrainian Su-25 fighter jet was shot down on Wednesday.
3. Is Crimea related to the latest escalated violence?
Crimea is more than 300 miles southwest of the rebel-held eastern part of Ukraine.
In March, Russian President Vladimir Putin argued that a group of anti-Russian extremists in power in Ukraine were a threat to Russian-speaking people who lived in Crimea, which was made up of about 60 percent Russian people.
Putin called the events in Ukraine an illegal coup and ordered troops into Crimea. Putin told Germany Chancellor Angela Merkel that he needed to protect ethnic Russians in Crimea from "ultranationalistic forces" in Ukraine.
4. Who are the groups involved and who has control now?
Pro-Russia rebels, or separatists, have been fighting with Ukrainian government troops in eastern Ukraine. Russian authorities have claimed Crimea as Russian territory while the Ukrainian government claims Crimea is still a part of its country.
On March 16, a "referendum" for the integration of Crimea into the Russian Federation was held but called illegitimate by the Ukrainian government, the EU, the U.S. and the U.N. General Assembly.
In elections in May, Petro Poroshenko, a billionaire tycoon in the chocolate business who is described as pro-European, became president of Ukraine.
5. How has the U.S. become involved?
Soon after Putin ordered troops into Ukraine, the U.S. announced in March a $1 billion loan guarantee to help Ukraine’s bank and finance ministry with its financial affairs and help prepare the country for its national elections in May.
On Wednesday, President Barack Obama announced sanctions against Russia, hoping to end the pro-Russia insurgency in eastern Ukraine. The sanctions target two major energy firms, financial institutions, eight weapons firms and four individuals.