Russia has accused the United States and NATO of what it called "provocative" statements as the crisis in Ukraine unfolds alongside a NATO military build-up in eastern Europe.
Meanwhile, diplomatic efforts are continuing to seek the release of seven observers from the Organization for Security and Cooperation in Europe, who are being held by pro-Russian gunmen in eastern Ukraine.
Transport planes brought about 130 U.S. Army paratroopers to Estonia on Monday, part of a NATO show of force in eastern Europe. Several NATO members have sent warplanes and ships to the region.
Russian Defense Minister Sergei Shoigu said Tuesday the military build-up was accompanied by "provocative" statements about the need to "contain" Russia.
NATO commander in Europe, General Adrian Bradshaw, insists the deployment is appropriate.
"Our judgment is that the actions that we have taken at the moment are proportional and appropriate to the changed security dynamic that we face. It gives a very clear indication on NATO commitment to the region," he said.
Russia is also building up its forces in the region. Two naval vessels have returned to join Moscow's Black Sea fleet based in Crimea, the region Russia annexed from Ukraine last month.
The highest tensions since the Cold War have prompted accusations of covert military intervention in Ukraine from both Russia and the West.
Seven observers from the OSCE were seized by pro-Russian gunmen last week in the flashpoint city of Slovyansk, accused of being NATO spies. Five Ukrainian soldiers were also taken hostage.
The observers were paraded in front of television cameras Sunday. The leader of the mission, German Army Colonel Axel Schneider, said they were in Ukraine strictly in line with their OSCE mandate.
"I clearly state the Vienna document[ed] diplomats come to the nation without arms, without ammunition. We are not fighters. We are diplomats in uniform," he said.
The militants want to exchange the OSCE captives for pro-Russian activists held by the Ukrainian government. Among the hostages are three German soldiers and one interpreter.
Berlin's Defense Minister Ursula von der Leyen visited their home barracks Monday.
She told reporters this was the first time that inspectors were apprehended during such a verification mission of the OSCE. She added "that's why it is all the more important to make clear that we will not be bullied and this will not jeopardize further missions. Quite the contrary."
The Vienna-based OSCE was created during the Cold War as a forum between East and West. Observer missions often include army personnel, but their role is strictly diplomatic, said Andrew Foxall of the Henry Jackson Society, a Britain-based policy analyst organization.
"To evaluate events on the ground, to monitor how the situation is developing, and then to make suggestions and policies for how the situation might then develop," he said.
The OSCE's 57 members include Russia. Western countries say it is up to Moscow to put more pressure on the pro-Russian gunmen to release all the hostages.
In a statement Tuesday, the OSCE said it was pressing ahead with plans to recruit hundreds of more monitors for a civilian mission in Ukraine, despite the detention of the seven military observers from a separate team captured by pro-Moscow rebels.