Ukraine's president has asked for discussions to begin on an action plan that could eventually lead to membership of Nato.
Petro Poroshenko said the will of the Ukrainian people was to eventually join the Western military alliance.
Nato Secretary General Jens Stoltenberg said any decision on future membership would be up to the 29 alliance members.
Russia has repeatedly criticised Nato's expansion in eastern Europe and objects to Ukraine becoming a member.
Ukraine faces many obstacles on the road to membership, including the conflict in the east of the country.
Mr Poroshenko was speaking after holding talks with Mr Stoltenberg in the Ukrainian capital Kiev.
"Ukraine has clearly defined its political future and future in the sphere of security," he said.
"Today we clearly stated that we would begin a discussion about a membership action plan and our proposals for such a discussion were accepted with pleasure."
Such a plan would set targets on political, economic and defence reforms.
But Ukraine could face bigger barriers, such as the demand that any international disputes should be settled by peaceful means, as stated by Nato rules.
That means having to resolve the situation in the Crimean peninsula, which was annexed by Russia in 2014, a move not recognised by the government in Kiev.
Given the challenges, analysts say any prospect of membership is still years away.
- Formed in 1949 to counter the threat of post-War communist expansion as the Soviet Union sought to extend its influence in Europe
- Originally consisting of 12 countries: Belgium, Canada, Denmark, France, Iceland, Italy, Luxembourg, the Netherlands, Norway, Portugal, the UK and the US
- The organisation expanded to include Greece and Turkey in 1952, West Germany in 1955, and Spain in 1982. However, then, as now, the alliance was militarily dominated by the US
- The Czech Republic, Hungary and Poland became the first former Warsaw Pact countries to gain Nato membership, in 1999
- Montenegro was the latest country to join the alliance, earlier this year. Before that, the most recent recruits were Albania and Croatia in 2009, and Estonia, Latvia, Lithuania, Slovenia, Slovakia, Bulgaria and Romania, which joined in 2004
- Applicant nations: Georgia, Bosnia-Hercegovina, Macedonia
Mr Stoltenberg said he welcomed the fact that Ukraine was moving towards meeting Nato standards, regardless of membership.
In a clear reference to Russia, he said that every nation could decide its own path and no-one else had the right to lean on them or veto the process.
He also called on Moscow to withdraw "thousands of soldiers" from Ukraine, despite Russia's denial of having any troops in the country.
Reacting to Mr Poroshenko's remarks, a Russian government spokesman, Dmitry Peskov, said: "For many years Russia has been worried by Nato's military infrastructure moving closer to our borders, potentially this could be the next step.
"It will not boost stability and security in the European continent."