In a statement, Merkel accused CDU leader Friedrich Merz of turning his back on a previous pledge not to work with AfD in the Bundestag.

The parliament descended into heckles on Wednesday after votes from the far-right party meant a non-binding CDU motion on tougher immigration rules was passed.

This is a highly unusual intervention by the woman who led Germany for 16 years, stepping in to criticise the actions of her former political rival.

Merz, who is tipped to be Germany’s next chancellor due to CDU’s lead in the polls, said on Wednesday that a policy was not wrong just because the “wrong people back it” and that he had not sought nor wanted AfD’s support.

But Merkel accused him of breaking a pledge he made in November to work with the Social Democratic Party and the Greens to pass legislation, not AfD.

This was to ensure “neither in determining the agenda nor in voting on the matter here in the House will there be a random or actually brought about majority with those from the AfD,” read a quote from Merz in Merkel’s statement.

The former chancellor said she fully supported this earlier “expression of great state political responsibility”.

“I think it is wrong to no longer feel bound by this proposal and thereby knowingly allow the AfD to gain a majority in a vote in the German Bundestag on 29 January 2025 for the first time.”

She said “all democratic parties” needed to work together “to do everything they can to prevent such terrible attacks in the future as those that took place shortly before Christmas in Magdeburg and a few days ago in Aschaffenburg”.

This is a rare intervention from Merkel.

To openly criticise her own party’s candidate for chancellor – just weeks out from an election – is a big move and will add rocket fuel to a an already explosive story in German politics.

Merkel and Merz go back a long way – and not as the best of friends.

He was famously side-lined by Merkel in the early 2000s after she won out in a CDU power struggle.

Merz would go on to quit front-line politics for many years before making his return.

Since then, he has criticized Merkel’s legacy – particularly her handling of the migration crisis.

They also have very different visions for the party, with Merkel seen as a more pragmatic centrist and Merz from the CDU’s more traditional, conservative wing.

Wednesday’s vote broke a longstanding taboo in German politics – and Merz is also due to propose legislation on Friday that the AfD could support.

The current German Chancellor, Olaf Scholz, called the move an “unforgivable mistake”.

“Since the founding of the Federal Republic of Germany over 75 years ago, there has always been a clear consensus among all democrats in our parliaments: we do not make common cause with the far right,” he said.