In light of Russia’s actions, we will draw all the necessary consequences for NATO’s deterrence and defence posture, NATO said in a statement.

"Allies have held consultations under Article 4 of the Washington Treaty. We will continue to take all measures and decisions required to ensure the security and defence of all Allies. We have deployed defensive land and air forces in the eastern part of the Alliance, and maritime assets across the NATO area. We have activated NATO’s defence plans to prepare ourselves to respond to a range of contingencies and secure Alliance territory, including by drawing on our response forces. We are now making significant additional defensive deployments of forces to the eastern part of the Alliance. We will make all deployments necessary to ensure strong and credible deterrence and defence across the Alliance, now and in the future. Our measures are and remain preventive, proportionate and non-escalatory.

Our commitment to Article 5 of the Washington Treaty is iron-clad. We stand united to protect and defend all Allies. Freedom will always win over oppression," the organisation said in a statement.

According to the alliance statement, the situation around Ukraine is "the most serious threat to Euro-Atlantic security in decades".

"We call on Russia to immediately cease its military assault, to withdraw all its forces from Ukraine and to turn back from the path of aggression it has chosen. This long-planned attack on Ukraine, an independent, peaceful and democratic country, is brutal and wholly unprovoked and unjustified. We deplore the tragic loss of life, enormous human suffering and destruction caused by Russia’s actions," the statement said.

Speaking after chairing the NATO summit, NATO Secretary-General Jens Stoltenberg said the organisation would send parts of the NATO Response Force and elements of a rapidly deployable forward element to the eastern flank of the alliance. This is the first time the force has been used to protect NATO allies, AP reported.