"I'm convinced that right now we are able to defend our territory from the first moment, from the first inch," Kallas told AFP at the start of a two-day summit in Lithuania.

Leaders are to sign off on new regional defence plans in Vilnius that will detail for the first time since the Cold War how each ally would help to defend NATO's vulnerable eastern fringe.

Shocked by the brutality of Russia's invasion of Ukraine, the alliance now says it is switching to a strategy that would halt Russia at its border rather than allow it to take territory.

Kallas warned ahead of NATO's summit in Madrid last year that her country would be crushed by Moscow's forces under previous alliance plans.

NATO countries have sent thousands more troops to NATO's eastern flank to allow them to respond more quickly to any aggression from Moscow.

"We moved from the deterrence posture to defence posture now we have the military plans that are implementing these decisions," Kallas said.

"What we have to do is fulfil those plans with actual capabilities and allies are doing this bit by bit."

Kallas insisted that it was vital that all NATO members fulfil a new pledge set to be unveiled in Vilnius to make two percent of their gross domestic product a minimum for defence spending.

The Estonian leader firmly backed Ukraine's push for membership in the alliance, but conceded that Kyiv would not join while war with Russia was raging.

"We really feel that Ukraine's place is in NATO because that is the only security guarantee that works and is the cheapest," Kallas said.

"We understand that it can't happen while the war is going on, and nobody's really demanding that, not even the Ukrainians, but we have to make sure that when all the conditions are met and we have the opportunity window when the war is over, then we can do this fast."

The United States, Britain, France and Germany are negotiating with Ukraine over future commitments on weapon supplies as an interim step before Ukraine joins.

Kallas called that a "short track" for while the conflict is ongoing.

But warned that earlier assurances given by the United States and Britain that convinced Ukraine to give up its nuclear weapons in the 1990s had not prevented Russia's attack.

"It is very important that you know, the assurances that the countries give are very practical," she said.

"What it really means, and for me, is that the West is behind Ukraine."