BRUSSELS — Russia's envoy to NATO warned Thursday that Moscow is concerned by the alliance's military deployment in the Baltic states and Poland, and will respond to the buildup, as thousands of U.S. and European troops trained on land, sea and in the air in central and eastern Europe.

"NATO is building a new military security situation that we cannot ignore, that we should address using our own military instruments," Ambassador Alexander Grushko said in Brussels.

He declined to spell out what kind of measures Russia might take, saying only that "NATO's movements will not be left without a response in terms of military planning."

Twelve NATO countries are deploying a total of about 4,600 troops to Estonia, Latvia, Lithuania and Poland, and the four battle groups are due to be fully up and running within two weeks.

NATO says it's a deterrent move aimed at countering aggression by Russia, which seized Ukraine's Crimean Peninsula in 2014.

"NATO is a defensive alliance, and we do not seek confrontation with Russia," NATO spokesman Piers Cazalet said. "NATO had no plan to deploy forces in the region before Russia's illegal annexation of Crimea."

Separately, about 4,000 U.S. and European troops from 14 nations were taking part in the annual Baltic Operations naval exercise that opened Thursday in the Baltic Sea port of Szczecin, in Poland, one of Russia's neighbors. The war games, which involve ground forces backed by about 50 ships and submarines and more than 50 aircraft, will run through June 16.

In Romania, meanwhile, another 2,000 soldiers, 1,000 assistance personnel and 500 vehicles from 11 NATO nations were training in the alliance's Noble Jump 2017 drill.

British troops stand near their vehicles after crossing the border from Bulgaria in Giurgiu, Romania, Thursday, June 1, 2017 to take part in the alliance's Noble Jump 2017 exercise which tests the readiness of alliance troops. Some 2,000 troops and more than 500 vehicles will head to the Cincu training area in central Romania from bases in Britain, Germany, the Netherlands, Spain, Poland, Norway and Albania, joining around 2,000 Romanian troops and over 1,000 enablers.

Photo Credit: Vadim Ghirda/AP

In a conversation with reporters that painted a bleak picture of NATO-Russia ties, Grushko also said that Moscow sees no shift in U.S. defense policy since U.S. President Donald Trump came to office.

"In real steps, there is not any change of U.S. policy through NATO vis-à-vis Russia," he said, noting that Washington has increased defense spending in Europe by 40 percent in its 2018 budget.

Grushko also questioned why European allies would boost spending, as Trump insisted they should during last week's NATO summit, when their combined defense budgets are already greater than Russia and China together.

He also said that the multitude of global threats means it's impossible for any group of states or organization like NATO "to create an island of security."

"If Europe is really interested in improving its own security, it is simply not possible to do it without Russia," Grushko said.

Following the summit and G-7 meetings last week, German Chancellor Angela Merkel suggested that Europe's relationship with the U.S. had shifted significantly, saying that "the times in which we can fully count on others are somewhat over, as I have experienced in the past few days."

Monika Scislowska reported from Warsaw, Poland.