Former German Chancellor Angela Merkel on Thursday issued rare public criticism of her successor as the country's center-right leader, the front-runner in Germany's election next month, for putting to parliament proposals for tough new migration rules that only passed with the help of a far-right party.

Germany's center-left governing parties have cast doubt on whether conservative leader Friedrich Merz can still be trusted not to bring the far-right Alternative for Germany, or AfD, into government after Wednesday's events.

Merz, determined to underline his center-right Union bloc's commitment to cutting irregular migration after a deadly knife attack last week by a rejected asylum-seeker, put a nonbinding motion calling for Germany to turn back many more migrants at its borders to a vote, although it might need AfD's votes to pass. The measure passed by a three-vote margin thanks to the far-right party's support.

Polls show Merz’s mainstream center-right Union leading with around 30% support, while Alternative for Germany is second with about 20%, and Chancellor Olaf Scholz’s center-left Social Democrats and their remaining coalition partners, the Greens, are further back.

Merkel, a former leader of Merz's Christian Democratic Union, noted in a rare statement that Merz had said in November that no measures should be passed with AfD's support before the Feb. 23 election.

She said she supported that position but "I think it was wrong no longer to feel committed to this proposal and, on Jan. 29, to enable with open eyes for the first time a majority with votes from AfD in a vote in the German parliament."

Merz took over the CDU after Merkel, a former rival, stepped down as chancellor in 2021. A more conservative figure than Merkel, he has taken a more restrictive stance on migration. He said last week that Germany has had a “misguided asylum and immigration policy” for a decade — since Merkel allowed large numbers of migrants into the country.

Merkel has largely kept a low profile since leaving office, doesn't usually intervene in day-to-day politics and is no longer actively influential in her party. However, her intervention could exacerbate a credibility problem for Merz.

Merz appears to hope that he will gain support by making the Union look decisive in forcing a tougher approach to migration, blunting the appeal of the anti-immigration AfD, while making center-left Chancellor Olaf Scholz and his remaining coalition partners, the Greens, look weak. It's uncertain whether that will succeed.