Jan M. Olsen

Associated Press

COPENHAGEN, Denmark (AP) — For the second time this year, a Russian military aircraft turned off its transponders to avoid commercial radar and nearly collided with a passenger jet over Sweden, officials said Saturday.

"This is serious. This is inappropriate. This is outright dangerous when you turn off the transponder," Swedish Defense Minister Peter Hultqvist said on Swedish radio.

Russia's Defense Ministry denied the claims Sunday.

In recent months, Russia has increased its military presence in the Baltic Sea area, prompting some Swedish officials to compare it to the Cold War. In October, non-NATO Sweden launched its first submarine hunt since the collapse of the Soviet Union. Swedish authorities said a small, foreign submarine had entered its waters illegally but never found it and didn't disclose its nationality.

NATO has air patrols over the Baltic Sea and the continuous rotation of NATO military units in and out of countries such as the Baltic states and Poland.

On Saturday, Swedish authorities said a Russian military aircraft nearly collided above southern Sweden with a commercial passenger jet that had taken off on Friday from Copenhagen.

Sweden's air force chief, Maj. Gen. Micael Byden, said the aircraft's transponders, which make the plane visible to commercial radar, were shut off. Swedish fighter jets were sent up to identify the aircraft, and Hultqvist later identified it as a Russian intelligence plane.

Byden said the incident in international air space looked "pretty serious," adding the southern-bound commercial flight was immediately ordered to change course. Media in Sweden and Denmark said the commercial plane was en route to Poland, but no one identified the airline that was flying the jet or how many people it was carrying.

Byden said this was not as serious as in March when a Russian plane flying without transponders came within 100 meters (300 feet) of an SAS plane that had taken off from Copenhagen.

Russian Defense Ministry spokesman Maj. Gen. Igor Konashenkov said Sunday the military aircraft was operating in compliance with rules governing international airspace and was flying at a safe distance from routes used by civilian flights.

"There were no prerequisites for an air accident," he said in a statement carried by Russian news agencies.

Konashenkov said the number of flights by NATO warplanes along Russia's borders has tripled in recent months, and a NATO reconnaissance plane was flying between the Russian aircraft and the passenger jet on Friday. NATO aircraft also fly in international air space with their transponders switched off, he said.

Carl Bildt, the former Swedish foreign minister, said this practice should be changed. "Should we seek an agreement for all military planes in international air in Baltic area to use transponders? For transparency and safety," he wrote in a Twitter post.

Contributing: Lynn Berry and Laura Mills, Associated Press