On Tuesday, leaders of the North Atlantic Treaty Organization (NATO) failed to set a timetable for Ukraine's membership of the alliance, following the first day of the NATO summit in the Lithuanian capital Vilnius.

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NATO Secretary Jens Stoltenberg said allies have agreed on a package of three elements to "bring Ukraine closer to NATO." However, he clarified that an invitation for Ukraine to join the alliance will be issued "when allies agree and conditions are met."

"It's unprecedented and absurd when a time frame is not set either for the invitation or for Ukraine's membership. While at the same time vague wording about 'conditions' is added even for inviting Ukraine," said Ukrainian President Volodymyr Zelensky, who is set to attend the inaugural meeting of the new NATO-Ukraine Council on Wednesday.

NATO members have been divided on how to bring Ukraine closer to their bloc. While some Eastern European members are pressing for an explicit commitment on when Ukraine will join, the United States and Germany are reluctant to clarify.

The tweet reads, "Ukrainian President Zelensky is greeted by NATO leaders at the Vilnius Summit during the first Ukraine-NATO Council meeting."

Stoltenberg said NATO leaders have also approved the "most comprehensive defense plans since the end of the Cold War," and endorsed a new defense action plan.

Under the new plans, NATO aims to have 300,000 troops fully ready for action. NATO allies have also made an "enduring commitment" to invest at least 2 percent of their gross domestic product (GDP) annually in defense, although after "nine consecutive years of increased defense spending" since 2014, only 11 out of 31 NATO members have reached or exceeded this target.

Critics argue that such an emphasis on militarization fosters an arms race among member states, diverting resources away from social and economic development and negatively impacting citizens' quality of life.

Swedish expert Jan Oberg said NATO's pledge to ask its members to invest a minimum of 2 percent of GDP annually on defense was "absurd." A military budget "should be decided according to a comprehensive threat analysis, followed by a priority discussion, and never be tied to a country's economic ups and downs," Oberg added.

"What we are seeing is a rampant, exclusivist militarism that doesn't care about the other side or about the consequences of its own provocative policies," said Oberg, director of the Transnational Foundation for Peace and Future Research.

Analysts have also warned that NATO's expansion and its responses to the Ukraine issue may seriously threaten global security.

Sevim Dagdelen, a member of Germany's lower house of Parliament, told Xinhua in a recent interview that NATO is not a defense alliance, although that is the constant refrain of Western leaders.

At the same time, the military pact is engaged in an aggressive arms drive and is thwarting all negotiation efforts regarding the Ukraine crisis, she said, accusing NATO of fighting a proxy war against Russia by supplying military aid to Ukraine.

On Tuesday, Kremlin spokesman Dmitry Peskov accused NATO of treating Russia like an "enemy." "We are clearly talking about the summit of an association, which has a pronounced, concentrated anti-Russian nature," Peskov said, adding that Moscow has witnessed repeated waves of NATO expansion towards its borders, and the West does not understand the risks of this expansion.

Ahead of the summit, protests against NATO have been held in several European countries. Underlining that the summit will see "calls for further escalation" of the Ukraine conflict, the Stop the War coalition organized a day of peace protests across Britain on Saturday.

Meanwhile, in Paris, a march against the military alliance drew hundreds of people, with many calling for France to withdraw from NATO.