Maris Riekstins, Latvia’s top envoy to NATO, said Wednesday the military alliance is not responsible for Ukraine’s security and should focus on protecting its member nations. NATO has taken steps in recent months to bolster its presence in Eastern Europe amid a marked increase in Russia’s military activity in the region.

“People often don’t understand why NATO doesn’t provide military assistance to Ukraine,” Riekstins said, according to the official Russian news agency Tass. “It’s worth recalling that NATO’s basic task is to protect the security of residents on the territory of the alliance members. Ukraine is a close partner of NATO, but, no matter how cynical this may sound, guaranteeing Ukraine’s security is not NATO’s duty.”

The military alliance has “no intention of acting outside the territories of its member-countries,” Riekstins said. The 52-year-old politician previously served as Latvia’s foreign minister and is considered a candidate for the nation’s presidency. He has been an outspoken critic of Russia’s foreign policy over the past several months.

Russian President Vladimir Putin has drawn international criticism over Moscow’s annexation of the former Ukrainian territory of Crimea in March last year, after pro-democracy protests topped that country’s pro-Russian president, as well as over Moscow’s perceived intervention in the ongoing conflict between Ukrainian government forces and pro-Russians in eastern Ukraine. More than 6,000 people have died since fighting began there last year.

The Latvian diplomat previously accused Russia of making false claims about NATO’s military expansion to justify its military action in Ukraine. “It is Russia that has brutally violated international law by exercising military power in its neighborhood,” Riekstins wrote in an open letter published in Foreign Affairs late last year.

Ukraine has repeatedly expressed interest in joining the NATO alliance. One of the nation’s top diplomats said NATO membership would be the only reliable check against Russian aggression in Eastern Europe.

“For the first time in history, a permanent member of the U.N. Security Council which possesses the nuclear weapon uses this factor to intimidate the international community and uses its military potential for annexation and seizing the territory of a European country,” Oleksandr Turchynov, head of Ukraine’s national security council, told NATO representatives in April, according to Reuters