German police have seized a bomb-loaded model plane they say neo-Nazis planned to use in an attack against left-wing activists.

It was discovered following a tip-off in the homes of four suspects and a neo-Nazi meeting place in south western Germany, prosecutors in the city of Freiburg said.

Although the plans appeared to be at a very early stage, the target was clear, a spokesman for the Freiburg prosecutor's office said. "They want to use it against left-wing or anti-Nazi activists."

A 23-year-old man with known links to far-right extremists was arrested on suspicion of commissioning the bomb. A 42-year-old man alleged to have built the bomb was detained but later released on bail. Police are also investigating two other men, aged 22 and 24, with far-right links as part of the case.

The main suspect, who was not named, had previously thrown a firework at anti-Nazi counter-demonstrators during a protest by a fringe far-right party.

But the bomb-rigged plane could have caused considerably more harm had it been used, said the prosecutor's spokesman. "It could have caused damage in a 20-30-metre radius," he said.

Official figures show Neo-Nazis committed over 800 violent crimes in Germany last year.