Russia said on Saturday that it had sent a fighter jet on Friday to intercept a US aircraft approaching its border over the Baltic Sea because plane’s transponder which is needed for identification was turned off.
According to the Pentagon, the Russian SU-27 fighter had intercepted the US Air Force RC-135 plane in an “unsafe and unprofessional” way, while the US plane had been flying a routine route in international airspace. The Russian jet had come within about 100 feet (30 metres) of the US plane.
"All flights of Russian planes are conducted in accordance with international regulations on the use of airspace," the Russian Defence Ministry said in a statement.
"The US Air Force has two solutions: either not to fly near our borders or to turn the transponder on for identification."
NATO has said it plans its biggest build-up in the region since the Cold War to counter what it considers to be more aggressive Russia. The incident on Friday underlined rising tensions between Russia and the United States over eastern Europe.
The Baltic states, Estonia, Latvia and Lithuania, which joined NATO in 2004, have requested higher and permanent presence of the alliance, fearing a threat from Russia after it annexed the Crimea peninsula from Ukraine in 2014.
The Kremlin denies any intentions to attack the Baltic countries, but it has often said that they have become an aggressive "Russophobic kernel" pushing NATO towards a consistently anti-Russian course.
"We are already starting to get used to the insults of the Pentagon regarding alleged 'unprofessional' manoeuvres when our fighters intercept US spy planes at the Russian border," the defence ministry said in its statement.