A joint declaration by NATO and European Union heads on the first day of the alliance's summit in Warsaw stressed that new new energy and substance must be invested in the NATO-EU strategic partnership.
Twenty eight members of NATO and the EU agreed that the unity of the Western world is the key to Europe's security and well-being.
European Council President Donald Tusk said, "There is no freedom in Europe without trans-Atlantic solidarity."
Tusk’s comment was a reference to a slogan favoured by Poland's anti-Soviet Solidarity freedom movement in the 1980s.
US President Barack Obama said security cooperation between NATO and the EU needs to be deepened and both bodies should increase support for Ukraine.
"In Warsaw, we must reaffirm our determination – our duty under Article 5 of the North Atlantic Treaty – to defend every NATO ally," Obama said.
"We need to bolster the defence of our allies in central and eastern Europe, strengthen deterrence and boost our resilience against new threats, including cyber attacks," he added.
Turkish President Tayyip Erdogan at the summit called on NATO to do more to fight the threat of global terrorism . He also stressed that the alliance needs to "update" itself to better adapt to new security threats.
"As we have seen from the terrorist attacks first in Istanbul and then in Iraq and Saudi Arabia, international security is becoming more fragile," he said.
Turkey, a member of NATO, is facing several threats to its security by the DAESH and PKK terrorist organisations and leftist militants. It is also a member of the US-led coalition against DAESH.
"The concept of a security threat is undergoing a serious change. In this process, NATO needs to be more active and has to update itself against the new security threats," Erdogan added.
‘UK won’t turn back on Europe’
Europe's biggest military spender is the United Kingdom, which decided last month to leave the EU but will continue to actively contribute to Western security.
"What I'll be saying is that Britain may be leaving the EU but we are not turning our back on Europe and we're not turning our back on European defence and security," British Prime Minister David Cameron told reporters on arrival for his final appearance at a NATO summit before stepping down as leader of the UK.
"The backdrop to this summit is the historic decision taken last month to leave the European Union but this summit will be an opportunity for us to demonstrate the enormous contribution that Britain makes to Europe's and NATO's security and that we will continue to do so even outside of the EU," a British government official said.
Russia’s ‘hybrid’ threats
The Alliance agreed to deploy four battalions totaling between 3,000 and 4,000 troops in the Baltic states. The US will send 1,000 extra troops to reassure Poland and its Eastern European allies against Russian aggression.
NATO and the EU pledged to intensify cooperation against propaganda and psychological campaigns, cyber-attacks, and use of political, economic and energy pressure, which they refer to as "hybrid" threats.
The declaration said the two bodies would "Step up our coordination on exercises, including on hybrid, by developing as the first step parallel and coordinated exercises for 2017 and 2018,"
Following Russia's invasion and annexation of Ukraine's Crimea Peninsula in 2014, Western countries decided to deploy troops and intensify security in the Baltic Sea and littoral states.
Russia’s support to rebels in Ukraine;s Donbass region has concerned Western countries.
Obama called on the EU and allied countries to maintain dialogue with Russia but also to maintain sanctions against Moscow until Russia fully complies with the Minsk agreements reached between Germany, France, Russia and Ukraine.
Ukraine is not a NATO member but President Petro Poroshenko will meet leaders of allied countries on Saturday.
Kiev fears that Moscow may try to destabilise Ukraine's pro-Western government with cyber attacks, stirr up Russian speakers with hostile broadcasting, and even make incursions into the country's territory.
NATO chief Jens Stoltenberg said that the Alliance doesn’t seek confrontation, adding it will continue talking with Russia.
"We don't want a new Cold War. The Cold War is history and it should remain history," he said.
However, Russia's ambassador to NATO, Alexander Grushko, warned of the creation of a "new Iron Curtain" and a "spiral of confrontation" emerging.
He told the BBC that this would lead to "military consequences."