NATO Secretary General Jens Stoltenberg says that the Alliance has been increasing its military presence at its eastern flank because of Russian aggression.

"[NATO's actions are] a response to what Russia did in Ukraine. Nobody talked about this kind of military presence before Ukraine. It doesn't justify any reaction from Russia, because it's always defensive from the NATO side. Russia has shown it is willing to use military force against sovereign nations in Europe with its aggressive actions against Ukraine and the illegal annexation against Crimea. And that's the main reason we are increasing the military presence in the eastern part of the alliance," he told journalists before the Warsaw NATO Summit opened on Friday.

When outlining NATO's plans, he said: "We will decide to increase our forward presence in the eastern part of the Alliance with four new battalions, multinational robust battalions and they will send a clear message that an attack on one Ally will be an attack on the whole Alliance. And we will also increase our presence in the south-eastern part of the Alliance, with tailored multinational presence," he said.

In his words, NATO does not seek confrontation and does not want a new Cold War. "The Cold War is history, and it should remain history. But we have to be able also in a more challenging security environment to defend and protect all our Allies," he added.