(CNN) A far-right German lawmaker has been beaten unconscious by at least three masked assailants in an attack seen by police as "politically motivated."

Frank Magnitz, a member of parliament and the leader of the anti-immigration Alternative for Germany party (AfD) in Bremen, was assaulted on Monday afternoon as he walked through the center of the city.

Masked men knocked him unconscious with a piece of wood "and kicked him further" in the head as he lay on the ground, AfD wrote in a statement.

A graphic image of the 66-year-old lying unconscious in a hospital bed was released by the party. It showed a large gash on his forehead, and his face was swollen and covered in blood.

Bremen police, who have begun an investigation into the assault, said two craftsmen called an ambulance after discovering Magnitz lying on the ground.

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