Ukraine's parliament has voted to drop the country's non-aligned status and work towards Nato membership.
Russian Foreign Minister Sergei Lavrov called the move "counterproductive" and said it would boost tensions.
The BBC's David Stern in Kiev says it is not clear when Ukraine will apply for Nato membership and many officials see it as a distant prospect.
Ukrainian President Petro Poroshenko pledged to seek Nato membership over Russian support for rebels in the east.
Russia, which annexed the Crimean peninsula in March, denies supplying the rebels with weapons. However, it is subject to EU and US sanctions over the crisis.
In a vote in Ukraine's parliament on Tuesday, MPs overwhelmingly backed the move by 303 to eight.
Speaking before the vote, Foreign Minister Pavlo Klimkin said Ukraine was determined to pivot towards Europe and the West.
Read more:
http://www.bbc.co.uk/news/world-europe-30587924Bit late.
