A Russian fighter flew "within several feet" of an Air Force reconnaissance aircraft over the Baltic Sea Monday, the latest in a series of alarmingly close encounters between the two militaries.

Capt. Joe Alonso, a spokesman for U.S. European Command, said in an email that the RC-135U Combat Sent airplane was flying in international airspace when it was intercepted by the Russian SU-27 Flanker.

"Due to the high rate of closure speed and poor control of the aircraft during the intercept, this interaction was determined to be unsafe," Alonso said.

Fox News, which first reported the incident, said that the Russian fighter was armed with air-to-air missiles and came within five feet of the RC-135U. EUCOM did not specify how close the fighter came to the plane, or say whether it was armed.

The encounter comes at a time of rising tensions between the two nations. A Navy F/A-18E Super Hornet shot down a Syrian SU-22 fighter on Sunday, prompting Russia — an ally of Bashar al-Assad's government — to cut off a deconfliction hotline meant to avoid mid-air collisions, and warn that all coalition aircraft and drones flying west of the Euphrates River "will be followed by Russian air defense systems as targets."

In April, the U.S. fired Tomahawk missiles at a Syrian air base — which was also being used by Russia — in retaliation for the Syrian army's use of chemical weapons against civilians. Russians strenuously objected to the missile strike.

And U.S. and NATO aircraft have repeatedly had close encounters with Russian aircraft — some alarmingly close — over the last two years. For example, NATO aircraft had four separate close encounters with Russian planes in a single day in February, the Air Force said.

The RC-135U Combat Sent aircraft are intended to collect electronic reconnaissance information and send it to the president, secretary of defense, other Defense Department leaders, and theater commanders. There are only two Combat Sent planes in the Air Force inventory.