Ukraine's president has signed a bill dropping his country's non-aligned status but also signalled that a referendum will be held before seeking NATO membership.
The bill, which the Ukrainian parliament adopted last week and Petro Poroshenko signed into law on Monday, has angered Moscow which called it a threat to its own and Europe's security.
Poroshenko said he was working to reform the Ukrainian economy and its military forces to meet European Union and NATO standards, but he would leave it up to Ukrainian citizens to decide in a popular vote whether to join the NATO alliance or not.
"When we are able to conform to these criteria, the people of Ukraine will make up their mind about the membership,'' Poroshenko said and added that this would likely happen in the next five to six years.
Non-aligned statuses are a classification given to states such as Switzerland which refuse to join military alliances and thus play no part in wars.
Kiev first announced its intention of seeking the protection of NATO membership in August following what it deemed the open participation of Russia's military in a separatist war in Ukraine's eastern provinces.
The leaders of Ukraine, Russia, Germany and France will get together in Kazakhstan on January 15 to discuss a peace settlement, Poroshenko also said on Monday. This will be the first such high-profile summit on the conflict since June.