When they say "rebels", are they talking about Ukrainians who are fighting Russians or are they talking about Russians fighting Ukrainians?
Rebels would be the separatists would be the Russian special forces. The Ukrainians are not rebels in their own country.
Western Ukraine sees itself as part of Europe. Eastern Ukraine wants to maintain close relations with Russia.
Last February, they had a revolution, in which the Russian-sympathizing President Viktor Yanukovych was overthrown and driven out of the country. Russia condemned the western-leaning revolutionary government and took back historically Russian Crimea, which Khrushchev had transferred to Ukraine in 1954 (when it manifestly did not matter).
Folks in the Russia-sympathizing eastern parts of the country, centered on Donetsk, rebelled against the Kiev government, aiming to split the country.
Lately, the fighting escalated to the use of advanced ant-aircraft missiles. On Monday, the rebels shot down a Ukrainian Air Force AN-26 transport and captured the crew who bailed out. Today, they shot down what they thought was another Kiev AN-26, but it turned out to be MH17. Bad move!
Kiev claims the leader of the rebels, Igor Girkin/Strelkov, is a colonel in the GRU. Naturally, Moscow denies that. Obviously, there are questions about how the rebels obtained the anti-aircraft rockets and the training to use them.