NATO has launched one of its largest military manoeuvres in the Baltic states since tensions spiked with neighbouring Russia over its annexation of Ukraine's Crimean peninsula.
Around 4700 troops and 800 military vehicles from 10 countries including Britain, Canada and the United States are participating in the Sabre Strike exercises near the Latvian capital Riga.
Russia has voiced its objections to the manoeuvres, which move to neighbouring Lithuania on Tuesday.
The exercises come as Moscow's March annexation of Crimea and sabre rattling in the Russian exclave of Kaliningrad have sparked fear in the neighbouring Baltics.
Estonia, Latvia and Lithuania were unwilling Soviet republics until the 1990-91 collapse of the USSR. They joined NATO and the EU in 2004.
"The exercise is very important given the current security situation," Latvian Defense Minister Raimonds Vejonis told reporters on Monday, citing the Ukraine crisis.
Russia was quick to label the games an "act of aggression," according to the Interfax news agency.
"We can't take this military build-up by the alliance next to Russia's borders as anything but a demonstration of hostile intent," Russian Deputy Foreign Minister Vladimir Titov told Interfax.
"The deployment of extra NATO troops in Central and Eastern Europe, even on a rotational basis is a violation of Russia's agreements with the alliance."
The US Air Force has deployed two nuclear-capable B-2 stealth bombers to a British air base for the exercises.
The deployment, the Pentagon said on Monday, was pre-planned and short-term.
"It certainly is yet another demonstration of America's ironclad commitment to the NATO alliance," said Colonel Steve Warren.
US military deployments have increased in recent weeks as Washington seeks to reassure Eastern European allies worried about Moscow's moves in the region.
The two B-2 bombers arrived on Sunday at RAF Fairford in Gloucestershire where they joined three other B-52 strategic bombers that got there on June 4.
The exercises are being held in the Baltic states from June 9 to 20. Denmark, Finland and Poland are among the other NATO members involved.
