Russia said emphatically on Tuesday it did not want Ukraine to become a NATO member, describing such a possibility as an "unprecedented challenge to European security".

"Ukraine in NATO would be an unprecedented challenge to European security, the biggest since the collapse of the Berlin Wall," said Vladimir Chizhov, Russia's envoy to the European Union.

Kiev announced its intentions to relaunch negotiations to join the Western military alliance in August, effectively restarting a process which was suspended in 2010 by pro-Kremlin president Viktor Yanukovych.

NATO has left the door open to membership for Ukraine on condition that it meets certain criteria.

Despite Russia's misgivings, the alliance has already welcomed several former Soviet states into its fold, including three Baltic nations -- Latvia, Lithuania and Estonia.

Kiev's tilt towards the West, including the signing of an association agreement with the European Union, sparked the current crisis with Russia.

Moscow responded by annexing Crimea and now stands accused of direct involvement in the conflict ripping apart eastern Ukraine -- a charge it denies.

On Tuesday, Russia's envoy reiterated a warning to the EU against imposing sanctions over the Ukraine crisis.

"Our message to the EU is: don't undermine the Ukraine peace process by supporting the party of war in Ukraine," said Chizhov.

"Only the UN Security Council has the right to impose sanctions. But sanctions have never been an effective tool.

"The EU's unilateral measures against Russia are wrong, unfair and misleading, based on the assumption that Russia is part of the conflict. It never was, it is not and will never be," said Chizhov.