Herrmann, of Bavaria's ruling Christian Social Union (CSU), the sister party to the Christian Democratic Union (CDU), told news agency DDP that he believed the socialist Left party to be "partly anti-constitutional."
Among other points, Herrmann said the Left party leadership supported "the cooperation with violent left-wing extremists." He added that there had been no development in the party which "offers a reason to stop observation by the constitutional protection office."
Herrmann expressed concern over the rising wave of left-wing violence in Germany, directed primarily at police officers as representatives of the state.
"It is a shame that left-wing violence is not condemned in public life with the same force as right-wing violence," Herrmann said. "Sometimes it is even trivialised." He added that fighting neo-Nazi violence did not justify supporting potentially violent people.
He called for government programmes aimed at combatting right-wing extremism to be implemented for left-wing extremism as well.
Hans-Peter Friedrich, chairman of the CSU's national committee in the German parliament, accused Berlin's mayor Klaus Wowereit of not doing enough against the recent spate of car-burnings in the capital. "The city should not trivialise this politically motivated criminality," he said in parliament. "The borders with terrorism are fluid when it comes to car-burning."
Herrmann also repeated his call for a ban on the far-right nationalist party the NPD. The NPD "must disappear from the political map," Herrmann said, "Any legal means for achieving this are justified."