Russia's increased military assertiveness was high on the agenda as U.S. President Barack Obama hosted the leaders of five Nordic countries at the White House.
"We are united in our concern about Russia's growing, aggressive military presence and posture in the Baltic-Nordic region," Obama said on May 13 at the end of the meeting with the leaders of Denmark, Iceland, Finland, Sweden, and Norway.
Obama said the six countries agreed on the need to maintain sanctions against Russia.
Earlier, Obama said that while willing to deescalate tensions, Washington would also be prepared to counter any perceived Russian aggression.
"We will be maintaining ongoing dialogue and seek cooperation with Russia but we also want to make sure that we are prepared and strong and we want to encourage Russia to keep its military activities in full compliance with international obligations," he said.
In a joint statement, the six countries expressed concern about Russia's actions in the Baltic Sea region, including "its nuclear posturing, its undeclared exercises, and the provocative actions taken by Russian aircraft and naval vessels."
The meeting came hours after U.S. and Polish officials symbolically broke ground for a new U.S.-led facility as part of NATO's European missile-defense shield in northern Poland.
On May 12, the United States activated a first-of-its-kind, ground-based missile-interceptor site in Romania, despite Moscow's protests.
Russian President Vladimir Putin warned on May 13 that U.S. antimissile systems in Europe will "force" Moscow "to consider putting an end to the threats emerging in relation to Russia's security."
Speaking at a meeting with military officials, Putin described NATO's missile-defense program as a threat to global security.
Putin said that Russia "will do everything needed to ensure and preserve the strategic balance, which is the most reliable guarantee from large-scale military conflicts."
However, Putin said that Russia would not get drawn into a new arms race.
Work on the site in Redzikowo in the north of Poland is to be completed at the end of 2018.
Situated some 250 kilometers from the Russian exclave of Kaliningrad, it will host 24 land-based SM-3 missiles as well as antiaircraft systems.
The installation in Poland is the final site of the European missile shield, which will be handed over to NATO in July and run from a U.S. air base in Germany.
With reporting by AFP, AP, Reuters, and dpa