NATO and the EU agreed on Thursday to work together more to counter "hybrid warfare" - the blend of unidentified troops, propaganda and economic pressure that the military alliance says Russia has used against Ukraine.
EU foreign policy chief Federica Mogherini also briefed NATO foreign ministers meeting in Turkey on her plans for an EU operation to destroy boats used to smuggle thousands of migrants from Libya to Europe. NATO said it would consider any request for help with the operation but the EU had not so far made any.
Critics have said the Ukraine crisis had shown NATO was ill-prepared to deal with unconventional tactics such as cyber attacks, information warfare and irregular militia.
Russian troops without insignia, dubbed "little green men," infiltrated Crimea before Moscow's annexation of the Ukrainian region last year.
NATO's military commmander, U.S. Air Force General Philip Breedlove, has said Ukraine has been the target of a broader diplomatic, propaganda, military and economic campaign.
NATO Secretary-General Jens Stoltenberg said he and Mogherini had agreed to "intensify NATO-EU cooperation in countering hybrid warfare".
"We will ensure that the strategies we are developing are complementary so that we can work together quickly and effectively in case of a hybrid threat against any of our members," he told a news conference.
NATO officials have been studying how they would respond to a Crimea-style operation in a Baltic ally such as Estonia or Latvia, which have large ethnic Russian minorities.
NATO and the EU are concerned by what they see as deliberate disinformation coordinated by the Kremlin over Moscow's role and aims.
Mogherini is working on an EU response that may include Russian-language broadcasts for ethnic Russians in ex-Soviet states.
"We ... face sophisticated disinformation and radicalization campaigns. Our best weapon against disinformation is information based on our values of democracy, freedom of speech and open societies," said Stoltenberg.
The EU is seeking United Nations authorization for a military operation to dismantle people-smuggling organizations and destroy their vessels to stop a migrant flow across the Mediterranean which has led to thousands of deaths.
"If the European Union presents requests to NATO, of course then we will seriously consider them and assess them, but so far there has been no request from the EU to NATO for any specific assistance [with the operation]," Stoltenberg said.
Veto-wielding Security Council member Russia has said it would be too extreme to destroy the smugglers' boats.
German Foreign Minister Frank-Walter Steinmeier expressed optimism on Thursday that Russia would let a resolution authorizing the EU mission go ahead.