Moscow on Thursday criticized Norway's plans to ask Washington to double the number of U.S. troops stationed in the Scandinavian country and deploy them nearer the border with Russia.
The plans "cause us serious concern," Russia's embassy in Norway wrote on its Facebook page.
Before joining NATO in 1949, Norway allayed Russian fears by pledging not to open its territory to foreign combat troops so long as it was not attacked or threatened with attack.
The stationing of U.S. troops in Norway "contravenes the Norwegian decision from 1949... This makes Norway less predictable, can stoke tensions, incite an arms race and lead to a destabilization of the situation in northern Europe," the embassy wrote.
But the Pentagon said Russia had no grounds for concern.
"Norwegian and Allied forces are training to defend Norway's territory, and pose no threat to Russia," Pentagon spokesman Eric Pahon said, adding that the U.S. presence complied with Norway's policy on the stationing of foreign troops.
The policy "does not preclude Allied exercises and training in Norway," he said in a statement.
Oslo's announcement came after nine nations along NATO's eastern flank last week called for the alliance to bolster its presence in their region.
Since last year, 330 U.S. Marines have been deployed on rotation at Vaernes in the center of Norway, despite loud protests from Russia.
Oslo now wants to boost the troop numbers to 700 and station them further north at Setermoen, 420 kilometers (260 miles) from Russia.
The U.S. deployment agreement would also be extended from the current six-month renewable periods to five years.
"The defense of Norway depends on the support of our NATO allies, as is the case in most other NATO countries," said Defence Minister Frank Bakke-Jensen in a statement.
"For this support to work in times of crises and war, we are totally dependent on joint training and exercises in times of peace," he added.
Bulgaria, Czech Republic, Estonia, Hungary, Latvia, Lithuania, Poland, Romania and Slovakia had Friday called for NATO to discuss an increased military presence in their region at next month's leaders' summit in Brussels.
The group said it was necessary to supplement NATO's current ground forces "with aerial and naval components."
NATO beefed up defenses in central and eastern Europe in response to growing fears about Russia, following Moscow's annexation of Crimea in 2014.
Norway has insisted that it is respecting its 1949 commitment, noting that the troop presence is not permanent but rotational.
But Moscow rejected that argument.
"Even if the actual people are rotated, the stationing is continuous," it said.
Russia also expressed "concern" that the "plans were agreed in Oslo without any real bilateral political dialogue."