Former Russian oil tycoon Mikhail Khodorkovsky has warned against further sanctions on Moscow for its role in Ukraine's current crisis.

In an interview with the BBC, he said Europe risked playing into the hands of nationalists trying to isolate Russia. Instead, he urged EU leaders to help Ukraine become more stable, saying this could encourage change in Russia.

Khodorkovsky was Russia's richest businessman until he fell out with the Kremlin and spent 10 years in prison. He has taken a keen interest in the crisis in Ukraine since being released and sent into exile abroad at the end of last year.

Khodorkovsky told the BBC that Ukraine had entered a "slow burn civil war" but he said he did not believe Russian President Vladimir Putin was planning to invade eastern Ukraine.

Putin had "lost control" of events in Russia's neighbor, Khodorkovsky said, citing the Kremlin's recent inability to stop a referendum by pro-Russian activists in Donetsk and Luhansk.

But he said Europe's reaction to events in Ukraine threatened to exacerbate renewed Russian nationalism, stirred up by the Russian president's annexing of Crimea.

Khodorkovsky argues that EU leaders should avoid further sanctions on Moscow and concentrate their efforts on encouraging political reform in Kyiv.

Russia could become even more authoritarian, he says, if the situation in Ukraine deteriorates and allows Putin to exploit a power vacuum in the country.

The BBC reminds Khodorkovsky is not without his critics.

He was seen by many Russians as one of the hated class of oligarchs, who made their fortunes in semi-legal circumstances in the chaotic years following the Soviet Union's collapse. But his arrest and long years of incarceration turned him from Russia's richest oil tycoon into the country's most famous political opponent of President Putin.