German Vice Chancellor Lars Klingbeil has backed an examination into banning the far-right Alternative for Germany (AfD) in an article written for the Die Zeit weekly and made public on Wednesday.

Klingbeil, co-leader of the centre-left Social Democratic Party (SPD), the junior partner in Chancellor Friedrich Merz's coalition government, also reaffirmed his support for maintaining the political "firewall" around the AfD to keep it from participation in government at all levels.

"It is intended to prevent enemies of the constitution from gaining political power. It protects the dignity of every individual and, with it, our liberal democracy. For me and for my party, this is non-negotiable," Klingbeil wrote.

The AfD, which is under investigation by German intelligence services for its extremist views, is the country's largest opposition party after finishing second in parliamentary elections last year.

The long-simmering debate over how to deal with the AfD has been reignited by a legal opinion commissioned by the Berlin-based advocacy group Society for Civil Rights (Gesellschaft für Freiheitsrechte). The report concludes that the party is "demonstrably unconstitutional."

Its eight authors, all of them legal scholars, argue that the AfD violates democratic principles and the constitutional guarantee of human dignity. More than 1,000 legal scholars and lawyers have also backed a public appeal calling for the party to be banned.

Klingbeil wrote that "independent scholars have demonstrated that the AfD is systematically working to destroy our democracy and the rule of law."

An application to the Constitutional Court to ban a political party may be made by either house of parliament or by the federal government.

Klingbeil's article was published as recent polls showed the AfD in the overall lead on around 27%, with Merz's conservative CDU/CSU alliance on around 23% and the SPD on around 12%.