Germany's former chancellor Angela Merkel has doubled down on her criticism of Christian Democratic Union, or CDU, leader Friedrich Merz over his willingness to cooperate with the far-right Alternative for Germany party in a parliamentary vote on immigration policy last week.

The unusual intervention from Merkel, who led the CDU for 18 years until 2018 and who was chancellor for 16 years until 2021, highlights growing tensions within Germany's conservative movement over its relationship with the increasingly powerful Alternative for Germany, or AfD, reported Agence France-Presse, or AFP.

Speaking at a live event hosted by Die Zeit newspaper on Wednesday, Merkel said she "thought it was right not to remain silent in such a decisive situation".

"I don't get involved in normal political debates, but I found this to be a question of fundamental importance," she added.

Last week, Merkel had said the conservatives' pledge not to work with the far-right was a "great national political responsibility".

Merz has attributed the AfD's growing popularity to Merkel's refugee policies, particularly her 2015 decision to welcome more than a million asylum seekers, predominantly from Afghanistan, Iraq, and Syria.

Addressing the rise of the far-right party during her tenure, Merkel acknowledged the AfD had gained support during migration policy disputes between her CDU and its Bavarian sister party, the Christian Social Union, or CSU. But she dismissed criticism of her policies, noting: "When I left office, the AfD was at 11 percent. The fact that it is now at 20 percent is no longer my responsibility."

Merz secured passage of a non-binding migration policy motion last week by accepting votes from the AfD. The legislation ultimately fell at the final hurdle before becoming law.

The decision to allow an anti-immigration motion to pass with AfD support in Germany's parliament triggered large protests across the nation on the weekend, because Merz had broken a long-standing taboo against cooperating with far-right parties, a principle known as the "firewall" that was established in post-war Germany.

While Merz has defended last week's immigration motion by claiming his party had not actively sought AfD support, Merkel referenced his November pledge against cooperating with the far-right.

Merkel had criticized her successor for abandoning his previous commitment to avoid AfD cooperation, saying it was "wrong" for Merz "to no longer feel bound by this proposal".

The dispute underscores the CDU's internal tensions over its stance toward the far-right as Germany approaches its Feb 23 federal election.

The latest polls show Merz's conservative CDU/CSU alliance leading with 30 percent of the vote, followed by the far-right AfD at 20 percent, while Chancellor Olaf Scholz's Social Democrats trail at 16 percent.

Merkel urged politicians to dial back tensions ahead of the elections.

"There is a degree of polarization (and) turmoil," she told an audience at the live event. "I think that has occupied every member of parliament. A state of affairs must now be found again in which compromises are possible, because it does not look as if any political grouping will get an absolute majority. This means that the democratic parties will have to talk to each other again."

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