A Russian Federation Air Force Su-27 Sukhoi intercepts a simulated hijacked aircraft entering Russian airspace in 2013. (Tech. Sgt. Jason Robertson/U.S. Air Force)

A Russian Su-27 multi-role fighter barrel-rolled over a U.S. spy plane operating in international airspace over the Baltic Sea last week, at one point coming within 50 feet of the U.S. aircraft, the Pentagon said Monday.

Navy Capt. Jeff Davis, a Pentagon spokesman, said the Russian jet went “from the left side of the aircraft, over the top of the aircraft and ended up on the right side of the aircraft.” He said the U.S. aircraft, an RC-135U, was on a routine mission at the time it was intercepted. Davis did not know if the Russian jet was armed.

[What it looks like when Russian attack jets fly ‘dangerously close’ to a Navy ship]

The close call comes less than a week after Russian Su-24 jets buzzed the USS Donald Cook, at some points coming within 30 feet of its deck while the destroyer was on a routine patrol in the Baltic Sea. The Su-24s were not armed.

In both instances, the Pentagon has decried the Russian maneuvers as unsafe and aggressive, maintaining that the the U.S. craft were operating in international airspace and waters, respectively. Russian officials played down the incidents.

“There have been repeated incidents over the last year where Russian military aircraft have come close enough to other air and sea traffic to raise serious safety concerns, and we are very concerned with any such behavior,” said Navy Capt. Daniel Hernandez, a European command spokesman, in a statement. 

The RC-135U is a converted Boeing jetliner and one variant of the RC-135 line of reconnaissance planes. The RC-135U is known as the Combat Sent and is designed to detect and collect electronic information broadcast from enemy positions, specifically radar emissions.

“On the one hand, the [RC-135 flight] is a part of a broader presence saying that ‘we’re here,’ ” said Peter Singer, a senior fellow and strategist at New America. “On the other, it’s soaking up all kinds of electronic information and seeing if there are any changes in the area.”

[A strange recent history of Russian jets buzzing Navy ships]

Russia maintains a modest naval base in the port of Kaliningrad on the Baltic Sea, and in recent months has reportedly moved S-400 surface-to-air missiles there. S-400s, called the SA-21 Growler by NATO, are also stationed at Russia’s main airfield in northern Syria. The S-400 relies on an advanced radar system to locate its targets and has the ability to intercept aircraft hundreds of miles from its launch site. S-400s located in Kaliningrad would be able to strike into the airspace over neighboring NATO countries such as Lithuania, Latvia and Poland.

The recent fly-bys of U.S. ships and aircraft by Russian jets are nothing new. Aside from repeated incidents in recent years, especially after Russia’s intervention in Crimea and Ukraine, the “Top Gun”-style antics were a hallmark of the Cold War. The frequent close calls prompted both countries to create formal and informal agreements that dictated how Russian and U.S. aircraft and ships would conduct themselves in the skies and on the sea.