It will take several years of work and a nationwide referendum for Ukraine to meet the minimum standards required to join the NATO military alliance, Ukrainian President Petro Poroshenko said Tuesday. Ukraine is one of several Eastern European nations whose leaders have broached the possibility of joining NATO amid an increase in Russian military aggression in the region.

“We have been working on a fundamental reform of the country in economic, social and administrative terms. It will take at least six, seven years of hard work [to meet the requirements to join NATO]. When we are ready, a referendum will be declared to ask the people of Ukraine whether we should join the North Atlantic Alliance,” Poroshenko told the Italian newspaper Corriere della Sera, according to the official Russian news agency Tass. He did not provide information on what Ukraine has accomplished so far.

Poroshenko personally supports Ukraine’s entry into NATO. He said, “There is no other system in the world but NATO that is capable of ensuring security.”

NATO requires potential entrants to meet certain criteria, including a demonstrable commitment to democracy and a free-market economy, civilian oversight of its military forces and a proven record of peaceful diplomacy, according to a 1997 U.S. State Department memo. NATO must feel as though the country’s addition will strengthen the alliance and improve global security.

Growing proportions of Finnish and Swedish citizens have called on their countries’ leaders to consider applying to join NATO. Several Eastern European nations, including Poland and the Baltic states of Estonia, Latvia and Lithuania have strengthened their ties with NATO in recent months and agreed to host elements of its military arsenal, despite Russian threats of retaliation.

Pro-democracy demonstrations forced former Ukrainian President Viktor Yanukovych to step down in early 2014 amid allegations of corruption and ties to the Kremlin. Soon afterward, Russian President Vladimir Putin ordered the annexation of the formerly Ukrainian territory of Crimea, in the face of international criticism.

Since Poroshenko took power, Ukraine has pursued closer economic and military ties with Western countries, including members of NATO. Ukraine’s leaders have been at the forefront of Western accusations about Russia’s purported support of separatists in eastern Ukraine during a conflict that has killed more than 6,400 since early last year.