A Seoul criminal court has sentenced dissident scholar Song Doo-yul to seven years in prison for violating the national security law.

The prosecution had earlier demanded a 15-year term for Song, a South Korean-born sociology professor at Muenster University in Germany, for his pro-North Korean activities.

A senior judge said upon issuing the ruling that the court could confirm that the defendant served as an alternate politburo member of North Korea's ruling Workers' Party.

After the ruling, defense lawyers said they would appeal the sentence.

The 59-year-old scholar had been under investigations after returning to Seoul in September after spending nearly four decades in self-imposed exile in Germany.

The professor had earlier acknowledged meeting North Korea's former president Kim Il-sung, contacting North Korean academics and receiving money from the North.