Washington(CNN) The repeated close encounters between Russian and U.S. warships and planes may not be an accident.
That's the view of analysts who are coming to believe that the risky Russian maneuvers -- there have been at least six close calls this year -- are part of Vladimir Putin's strategy aimed at challenging the U.S.'s global position and intimidating its European allies.
"The Russians believe that if they do a show of force, that they achieve results that promote their interests. In this case, it is a certain degree of intimidation," retired Army Gen. Wesley Clark told CNN.
Clark, who was NATO's supreme allied commander until 2000, added that it "shows that they (the Russians) are willing to stand up to the United States."
The Kremlin has been angered lately by NATO's effort to bolster its eastern flank amid increased Russian military activity in the region.
The Russian-U.S. military episodes have taken place all over the world, from the Pacific Ocean and Mediterranean to the Baltic and Black Seas.
In the most recent incident, a Russian ship last week came within 150 yards of a U.S. Navy vessel, the USS San Jacinto, that was sailing in the eastern Mediterranean. The U.S. Navy described the maneuver in a statement as unsafe, "erratic" and "aggressive."
A few weeks earlier, the Russian Neustrashimyy-class frigate came within 315 yards of the USS Gravely.
And in April, two Russian fighter jets flew within 30 feet of the USS Donald Cook while it was sailing in the Baltic Sea, an action that U.S. Secretary of State John Kerry warned could have led to the jets being shot down.
U.S. officials say Russian warship came dangerously close
Kerry told CNN en Español that "under the rules of engagement, that could have been a shoot-down, so people need to understand that this is serious business."
Many see the spate of incidents not as accidents but as intentional moves by the Russian president.
Heather Conley, of the Center for Strategic and International Studies, a DC-based think tank, told CNN after the April incident that Putin is trying to send a message to America's partners.
"To America's European allies, the Kremlin is messaging that the U.S. cannot protect them from Russia if Russia wants to do something to them militarily," she said.
The latest close calls come as the U.S. and NATO take steps to reinforce the alliance's eastern flank in the days leading up the summit of leaders, to take place in Warsaw, Poland on July 8-9.
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Last month, NATO announced the alliance would deploy four multinational battalions of about 1,000 troops each to Estonia, Latvia, Lithuania and Poland as part of a bid to deter Russia in the wake of Moscow's intervention in Ukraine and annexation of Crimea in 2014.
The Kremlin has lambasted NATO's eastern activity and has announced plans to deploy advanced nuclear-capable missiles in its European enclave of Kaliningrad by 2019, according to Reuters.
And Putin warned Finland this week against joining NATO, telling reporters after a meeting with the Finnish president that if the country became part of the Western military bloc, "Do you think we will keep it as it is? Our troops at 1,500 (kilometers, 900 miles) away?"
"Russia of course is trying to push back against the United States wherever it can," Michael O'Hanlon, senior fellow in foreign policy at the Brookings Institution, told CNN.
But he noted that the strategy poses significant risks.
"When he starts operating planes and ships near our major vessels on the water there is a potential for a major ship disaster," he said.
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