Shortly before his visit to the region, President Vladimir Putin accused the U.S. of destabilizing the Balkans.
The Senate is ready to fight to keep the U.S. in NATO.
"A serious breakthrough has been made in developing advanced and unparalleled weapons," Russian President Vladimir Putin said.
"We have the corresponding forces of our submarine fleet there," a defense expert warned. But he argued that Moscow simply does not wish to "show off in such a silly way."
"We don't want to be disappointed in our [U.S.] colleagues again, and therefore we are assuming the worst-case scenario in our military planning," Russia's deputy foreign minister said.
"I don't think the French expect me to respond to tweets," the country's president said.
Russian Prime Minister Dmitry Medvedev called NATO's 2011 intervention in Libya "a cynical deception" and said Moscow was "ready to cooperate" on peace initiatives.
The German chancellor's support of French President Emmanuel Macron's calls for a unified European force came as U.S. President Donald Trump criticized the idea, mocking France's loss to the Nazis in World War II.
"Russia is known to possess such capabilities," said Finnish Prime Minister Juha Sipila.
"For over five years, the United States has pursued diplomatic and technical avenues with Russia aimed at preserving the INF Treaty," NATO Secretary-General Jens Stoltenberg said.
Around 50,000 troops, 65 vessels, 150 aircraft and 10,000 vehicles will take part in Trident Juncture 2018.
All of NATO's 29 members will take part in the exercises, as will the alliance's partners Sweden and Finland.
U.S. Navy Admiral James Foggo said one of the exercise's messages was to "show NATO is capable of defending, it is capable of deterring any adversary."
"It is time now for Russia to come to the table and stop the violations," the U.S. ambassador to NATO told reporters.
The bombers were "a hazard to all other aviation," the Ministry of Defence said.