Su-27 på tur igjen - Svartehavet denne gang - CNN

(CNN)A Russian fighter jet came within 15 feet of a U.S. Air Force reconnaissance plane over the Black Sea this week in what the Pentagon is calling an "unsafe" incident, U.S. officials say.

"On January 25, 2016, a U.S. RC-135U flying a routine route in international airspace over the Black Sea was intercepted by a Russian Su-27 in an unsafe and unprofessional manner. We are looking into this particular incident," said a statement from Army Lt. Col. Michelle L. Baldanza, a Defense Department spokesperson.

Another U.S. military official told CNN that the Russian jet flew along the right side the U.S. plane then turned away in a maneuver that had an adverse impact on the "controllability of the U.S. aircraft." The official did not know if the Russian aircraft was armed at the time. The official said the incident occurred more than 40 miles from the Russian coast.

The U.S. official said Russian intercepts happen routinely and the majority are conducted safely.

But Monday's encounter is similar to one between the same two types of U.S. and Russian aircraft in 2014.

In that incident, a Russian Su-27 flew within 100 feet of the nose of the U.S. Air Force RC-135U over the Sea of Okhotsk between Russia and Japan, a Defense Department official said.

At the time, the U.S. official called it "one of the most dangerous close passes in decades" and said the Russian jet "put the lives of the U.S. crew in jeopardy."

The Russian aircraft turned and "showed its belly" to the U.S. crew so they could see it was armed with missiles.

The RC-135U is a four-engine jet used in "locating and identifying foreign military land, naval and airborne radar signals," according to the Air Force.

The jet "collects and minutely examines each system, providing strategic analysis for warfighters. Collected data is also stored for further analysis by the joint warfighting and intelligence communities," the Air Force says.

The RC-135U carries a crew of 21, including 10 electronic warfare officers, an Air Force fact sheet says.

There are only two RC-135U aircraft in the Air Force inventory.