U.S. military plane entered Swedish airspace without permission

WASHINGTON, Aug. 2 (UPI) -- A U.S. Air Force spy plane ended up in Swedish air space without permission last month after the Russian military began tracking the plane, U.S. military officials said.

The RC-135 Rivet Joint plane was flying in international airspace July 18 to eavesdrop on the Russian military when Russia began tracking the plane using land-based radar, a U.S. official, whose name wasn't reported, told CNN.

The U.S. aircraft retreated into Swedish airspace without approval after Russia sent a fighter jet to intercept the RC-135 Rivet Joint plane.

Officials from the United States are discussing the incident with Sweden, including the possibility it may happen again in the future if a U.S. plane has to quickly divert away from Russian activity.

The official said the Russian tracking was unusual.