The incident took place last Monday, when the U.S. reconnaissance jet was flying in international airspace, EUCOM spokesperson Meghan Henderson told CNN.

According to the U.S. official, the Russian fighter jet was armed and flying erratically and, given the close proximity of the two aircraft, such maneuvers were deemed unsafe.

The two jets were flying close enough together that the Russian pilot can clearly be seen in the fighter jet's cockpit.

The Russian Ministry of Defence rejected these accusations, however, claiming that it was in fact two U.S. reconnaissance jets who approached the border of Russian airspace.

"When being escorted, the RC-135 made a provocative effort to approach the Russian fighter jet," the Russian ministry told Russian News Agency TASS, adding that ten minutes later another U.S. RC-135 reconnaissance jet appeared in the area and the Russian Su-27 began to escort the second plane as well.

According to the U.S. official who spoke with CNN, there have been approximately 30 incidents near the Baltic Sea since the beginning of June in which Russian and U.S. aircraft and ships have come in close contact. The majority of these contacts, however, have been safe and professional, she added.

Pentagon spokesperson Capt. Jeff Davis noted that this made the June 19 incident unusual, especially as the U.S. had not done anything provocative in international airspace.

The unsafe approach by a Russian fighter jet to a U.S. reconnaissance jet was reported by Fox News in the first half of the week already, which was followed by Moscow's accusations that a NATO jet had reportedly flown too close to the plane of Russian Minister of Defence Sergey Shoygu and two accompanying aircraft.

NATO responded to this claim in turn by confirming in an emailed statement that their jets were scrambled to identify the aircraft according to standard procedure as they had not identified themselves or responded to air traffic control.