NATO does not want "a new Cold War" with Russia, Secretary-General Jens Stoltenberg said at the end of a four-day parliamentary assembly of the alliance.
"We are concerned by...[Russia's] lack of transparency when it comes to military exercises," Stoltenberg said on October 9 in the Romanian capital, Bucharest.
He mentioned the Zapad exercise that Russia held with Belarus in September, which brought thousands of troops close to NATO's eastern members and caused concerns about Moscow's intentions given its military interference in Ukraine.
At the same time, Stoltenberg said: "Russia is our neighbor.... We don't want to isolate Russia; we don't want a new Cold War."
He said the 29-member alliance has stepped up jet patrols over the Black Sea in "response to Russia's aggressive actions in Ukraine."
Romanian and Bulgarian pilots have conducted air exercises in the Black Sea in recent months, designed to reassure NATO members after Russia's interference.
Russia occupied and seized control of Ukraine's Crimean Peninsula in 2014, and backs separatists in a war that has killed more than 10,000 people in eastern Ukraine.
At the end of the parliamentary session in Bucharest, NATO also announced the launch of a new multinational force in Romania, its latest move to protect its eastern flank and to check a growing Russian presence in the Black Sea.
Initially, a small force composed mostly of troops from 10 NATO states including Italy and Canada as well as host Romania, the land, air, and sea deployments are expected to complement some 900 U.S. troops already in place separately throughout the country.
"Our purpose is peace, not war," Romanian President Klaus Iohannis told the session.
"We are not a threat for Russia, but we need a long-term NATO strategy; we need dialogue from a strong position of defense and discouragement," he said.
With reporting by Reuters and AP