Brussels, Jan 11 : The NATO and the EU signed a third Joint declaration on cooperation that aimed to further expand their strategic partnership collaboration and strengthen collective European defence. "We have just signed the third EU-NATO joint declaration ... This is more important than ever," NATO Secretary General Jens Stoltenberg told a news conference following the signing ceremony at the military alliance's headquarters in Brussels on Tuesday. The declaration was signed by European Council President Charles Michel and European Commission President Ursula von der Leyen, who lauded the agreement, saying it would deepen the existing cooperation between the Union and the alliance. According to the joint declaration, EU and NATO will expand and deepen cooperation in such areas as geostrategic competition, resilience, critical infrastructure protection, emerging and disruptive technologies, and space, Xinhua news agency reported. Von der Leyen said that Europe's security was "challenged" and "under threat" by the conflict in Ukraine. Stoltenberg highlighted the importance of the declaration, stressing the crucial role of NATO in Euro-Atlantic security. He noted that this declaration built upon two previous joint declarations signed in 2016 and 2018. Stoltenberg touched upon the prospect of Finland and Sweden joining NATO, stating that this would result in the alliance protecting 96 per cent of EU citizens. /IANS