Ukraine’s acquisition to the NATO bloc would be a declaration of war against Russia, and that global catastrophe can only be prevented through the alliance’s prudence, former Russian president Dmitry Medvedev said.

"This, in essence, would be a declaration of war - albeit with a delay," he said in remarks published on Wednesday, following NATO’s pledge to grant Ukraine membership at the summit in Washington last week.

Medvedev, Russia’s Security Council deputy chairman, told Argumenty I Fakty that Ukraine’s accession would pose more than just a direct security threat to Russia.

"The more such attempts there are, the harsher our answers will become," Medvedev said, responding to the bloc’s intent to advance their interests and expand the alliance. "Whether this will shatter the entire planet into pieces depends solely on the prudence of (NATO) side."

"For Russia, nothing will change, since key decisions are made not by NATO member countries, but by one state - the United States," Medvedev said regarding Mark Rutte’s appointment as the head of NATO.

The alliance was formed after World War Two, and was based on combatting the Soviet Union and its ideology. However, NATO’s recruitment of former Soviet states has been viewed as an act of aggression by the Kremlin, where Medvedev has warned the Western allies that their support of Ukraine may lead to a “nuclear apocalypse.”

Ukraine and NATO should disappear: Medvedev

Either Ukraine or the NATO alliance should disappear, former president Medvedev said on July 11, concerning the alliance's decision to grant Ukraine membership "irreversible."

“The conclusion is obvious. We have to do everything to make sure that the ‘irreversible path of  Ukraine’ towards NATO ends with either the disappearance of Ukraine, or the disappearance of NATO. Better, both,” Medvedev said on Thursday.

During the NATO summit in Washington DC, the bloc reiterated their support for Ukraine's “right to choose its own security arrangements,” proclaiming that it is on an “irreversible path to full Euro-Atlantic integration, including NATO membership.”

Russia has frequently stressed that the former Soviet state's adoption into the alliance is crossing a "red line," and that the European bloc was one of the main triggers for Russia's war with Ukraine.

Medvedev called for cautiousness should Ukraine accept Russia's terms for a ceasefire, including revoking their NATO aspirations. However, the politician warned that the acceptance of negotiated peace could spark internal unrest in Ukraine potentially a coup or the rise of a new radical government, reigniting hostilities between the two nations, while jeopardizing Ukraine's sovereignty.

If such an event should arise, Medvedev predicted that “the enemies of Russia will not go anywhere” and will “gather strength for a new attempt to destroy our country."