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HELSINKI, Finland (AP) _ The Finnish air force stepped up security Thursday after training planes came under fire in two separate incidents at a military airfield.

Both incidents on Tuesday and Wednesday involved Hawk jets making night landings at Kauhava, 260 miles northwest of Helsinki.

As the jets approached the airfield, an object, possibly a rocket, was launched from a nearby road, Col. Kai Vainio said. It was not clear how close the projectiles came to the aircraft.

He said no one has claimed responsibility but authorities believe the incidents are not terrorism.

``We aren't sure exactly what kind of projectiles were used but it seems we are talking about a rocket with a tracer,'' Vainio said. ``Nothing was hit, but we are taking (the attacks) very seriously.''

Vainio said security had been increased at the airfield, surrounded only by a light metal fence.

Investigators found pieces of piping that could have been used to launch the projectiles on a road some 200 yards from the runway, said Detective Chief Inspector Mikko Uusimaki.

The Nordic country of 5.2 million people was shocked by its worst violence since World War II when a 19-year-old bomber killed himself and six others, and injured 80, at a crowded shopping mall two weeks ago.