NATO leaders agreed on Friday that a large-scale cyberattack on a member country could be considered an attack on the entire U.S.-led alliance, potentially triggering a military response.
The decision marks an expansion of the organization's remit, reflecting new threats that can disable critical infrastructure, financial systems and government without firing a shot.
"Today we declare that cyber defense is part of NATO's core task of collective defense," NATO Secretary General Anders Fogh Rasmussen told a news conference.
In 2007, a series of crippling cyberattacks paralyzed much of NATO member Estonia in an apparent response to a dispute over the movement of a Soviet-era war memorial. Most Western experts suspected the Kremlin was responsible but Russia denied it.
NATO backs plan to boost alliance's defenses
NATO leaders also approved a plan on Friday to boost the alliance's defenses in eastern Europe in response to Russia's intervention in Ukraine, Rasmussen said.
The plan, adopted at a summit in Wales, includes creating a "spearhead" rapid reaction force and pre-positioning supplies and equipment in eastern European countries so they can be rapidly reinforced in a crisis.
Read MoreNATO:Russia 'attacking' Ukraine as chasm widens
The initiative is intended to reassure former Soviet bloc states that have joined the U.S.-led the alliance, especially Poland and the Baltic states of Estonia, Latvia and Lithuania.
The allies agreed to hold the next NATO summit in Poland in 2016 in a symbolic gesture of support, Rasmussen said.
NATO says no third country can veto membership
NATO, responding to Russian warnings against Ukraine's bid to join the Western alliance, said on Friday that no third country could veto its enlargement policy and approved new steps to advance Georgia towards membership.
"No third country has a veto over NATO enlargement," Rasmussen told a news conference on the second day of a summit of the U.S.-led defense pact, adding: "NATO's door remains open. Each country will be judged on its merits."
The 28-member alliance agreed on a package of measures to boost Georgia's defense capabilities and advance the former Soviet republic's preparations to join, he said. Russia and Georgia fought a brief war in 2008 after NATO agreed in principle that it and Ukraine would one day become members.
Rasmussen also said NATO stood ready, if requested, to help Iraq counter Islamic State fighters who have captured swathes of its territory and would cooperate on exchanging information on foreign fighters returning from the Middle East—a potential source of terrorism in Western countries.
Poland welcomes boost to NATO presence
Polish President Bronislaw Komorowski said on Friday his country greatly valued the decision by NATO to create the "spearhead" rapid reaction force that will boost the alliance's presence in eastern Europe.
"We value very highly the fact that there is a progress in increasing the level of NATO readiness to create ... (a spearhead), including assigned forces that comprise around 5,000 troops for absolutely immediate reaction," Komorowski told a news briefing at the summit.
NATO stands by pact with Russia despite violation: Merkel
NATO stands by a 1997 agreement on cooperation with Russia even though Moscow has breached it through its actions in Ukraine, German Chancellor Angela Merkel said Friday.
She told a news conference that alliance leaders agreed at the summit that the NATO-Russia Founding Act remained a key part of Europe's security architecture. Cooperation was suspended in March after Russia seized and annexed Crimea from Ukraine.
Merkel said new European Union sanctions, due to be adopted on Friday over what she called Russia's illegal troop presence in eastern Ukraine, could be suspended if a promised cease-fire materialized and the crisis de-escalated.
—By Reuters