Moscow itself has "voided of any content" the NATO-Russia Founding Act, by attacking Ukraine and halting dialogue with the alliance, Mircea Geoana told AFP.

Under the 1997 Founding Act, intended to reset the relationship between Russia and the Alliance, both sides agreed to work to "prevent any potentially threatening build-up of conventional forces in agreed regions of Europe, to include Central and Eastern Europe".

"They took decisions, they made obligations there not to aggress neighbours, which they are doing, and to have regular consultations with NATO, which they don't," said Geoana, speaking in the Lithuanian capital Vilnius.

"So I think that in fact this founding act is basically not functioning because of Russia," he added.

Russia, he said, had effectively moved away from the terms of the 1997 agreement.

"Now we have no restrictions to have robust posture in the eastern flank and to ensure that every square inch of NATO's territory is protected by Article 5 and our allies."

NATO's article 5 is the one referring to collective defence, which says that an attack on one member is an attack on all of them.

Geoana did not give details of any such planned deployment, but said he anticipated "a robust, flexible and sustainable presence".

In 2017, NATO had already deployed multinational tactical groups to the Baltic states and Poland as a dissuasive measure. After Russia's invasion of Ukraine at the end of February, it sent reinforcements there.

The Baltic states have called for a greater presence of its allies there, including for the development of brigades to replace the smaller tactical groups.

NATO defence ministers will meet in mid-June to discuss this and other questions, and the leaders of the NATO members states will meet to approve any changes at a NATO summit in Madrid at the end of June.