Speaking on Sunday in the German newspaper "Bild am Sonntag," Vice Chancellor Sigmar Gabriel said that AfD "belongs in the intelligence services report and not on TV."

"It's unbelievable that such parties are allowed to send out their slogans on public broadcasters," Gabriel told the newspaper.

In Germany, Gabriel said, there used to be a clear rule, "We do not help parties, who oppose the free democratic basic order of our country, to spread their propaganda on television."

"This does not concern the bizarre demands, like Petry's call for all women to have at least three children," said Gabriel, who is also the German economic minister and head of the Social Democratic Party (SPD). "Instead, this lady wants to let unarmed refugees be shot at."

Gabriel also said there were "huge doubts" that the AfD stood for the democratic principles Germany was founded on.

The vice chancellor's comments on Sunday came a day after AfD leader Frauke Petry said in an interview with the "Mannheimer Morgen" that German border guards "must prevent illegal border crossings and even use firearms if necessary."

"We need comprehensive controls to prevent so many unregistered asylum seekers from crossing the border," Petry said.

Warnings from history

The AfD leader's comments were immediately met with a backlash of outrage from both police and politicians. In a statement released on Saturday, German police union, GdP, said "no policeman would be ready to fire at" migrants.

"Whoever wants to deploy such methods clearly wants to suspend the rule of law," said GdP head Jörg Radek.

"We have already seen that over the course of German history, and we don't ever want to go down that road again," he added.

Parliamentary leader of the Social Democrats (SPD), Thomas Oppermann, said Petry had "completely lost her way politically."

"Her proposal is reminiscent of the firing order in the GDR," Oppermann said, adding that the "last German politician who was shooting at refugees was Erich Honecker," who led the former East Germany from 1971 until the fall of the Berlin Wall in 1989.

Echoing Oppermann's sentiments on Sunday, Gabriel said Petry, who was born in the eastern German city of Dresden, should know all too well what it means to shoot at people at a border.

Right-wing 'only good at protesting'

Also speaking to the "Bild am Sonntag," Chancellery chief and Christian Democrat Union member Peter Altmaier said he did not believe the AfD would be able to permanently establish itself as Germany's third-strongest political party.

"This alleged high will come crashing down if the challenge of the refugee crisis is overcome," Altmaier said. "These right-wing parties are only good at protesting and don't offer any solutions."

ksb/sms (Reuters, AFP, dpa)