Ambassadors of the European Union’s 28 member states have approved the decision to extend sanctions against Crimea for another year.
Thousands of troops from NATO and its partner nations are training on land and sea in central and eastern Europe.
Though he denied the Russian state had been involved in hacking, Putin said individual "patriotic" hackers could mount their own attacks.
Russian state gas exporter Gazprom, which supplies around a third of the EU's gas, is keen for Nord Stream 2 to be built by 2019.
The security and foreign policy of the European Union needs to be uniform, Estonian President Kersti Kaljulaid said during a meeting with Slovakian President Andrej Kiska in Bratislava.