Centre-left Chancellor Olaf Scholz told his election rival Friedrich Merz that any cooperation with the anti-immigration Alternative for Germany party would be an "unforgivable mistake".
Merz, who planned to file motions demanding tougher immigration rules, fired back at Scholz by recalling a series of bloody attacks blamed on asylum seekers and demanded: "What else needs to happen in Germany?"
"How many more children have to become victims of such acts of violence before you also believe there is a threat to public safety and order?"
Emotions are raw ahead of Germany's February 23 elections after a knife attack last week killed two people, including a two-year-old child. Police have arrested a 28-year-old Afghan man as the main suspect.
Merz, whose CDU-CSU alliance strongly leads Scholz's SPD in opinion polls, has vowed to go "all in" with demands to massively limit irregular immigration and permanently police all borders.
Controversially, he vowed to drive two motions through the Bundestag on Wednesday, if necessary with the backing of the AfD, which has signalled its support in what was expected to be a tight vote.
Scholz's SPD and the Greens have voiced alarm this would spell the end of a long-standing "firewall" of non-cooperation with the far right that all mainstream parties have so far adhered to.
Scholz told parliament that "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."
- 'Poisoned climate' -
Scholz urged the CDU not to accept support from "those who fight our democracy, who despise our united Europe, and who have been poisoning the climate in our country for years".
"This is a serious mistake -- an unforgivable mistake."
Merz, despite growing pushback also coming from human rights groups and churches, has argued the situation is so dire that he will take whatever support he can get.
He told parliament that the sight of "cheering and grinning AfD MPs will be unbearable" but maintained that "a correct decision does not become wrong just because the wrong people agree, it remains right".
Merz's bloc later planned to table two motions signaling a dramatic shift in German immigration and security policy.
The motions, which express intent but fall short of changing any laws, call for Germany to reject "all attempts to enter the country illegally without exception", including asylum seekers.
The push comes after Germany was stunned by news last Friday that a man attacked a kindergarten group with a kitchen knife in the Bavarian town of Aschaffenburg, where police arrested a 28-year-old Afghan suspect, who was later transferred to a closed psychiatric institution.
The attacker killed a two-year-old Moroccan boy and a German man who tried to shield the toddlers, and wounded three more people, including a two-year-old Syrian girl.
In December a Saudi man drove a car through a crowded Christmas market in Magdeburg, and there were also deadly stabbing attacks last year blamed on Syrian and Afghan men.
- 'Champagne on ice' -
More than a million refugees and asylum seekers, many from Syria and Afghanistan, came to Germany under former CDU chancellor Angela Merkel, whom Merz has strongly criticised. More than a million have also come from war-torn Ukraine.
Merz says that Scholz's government has done too little to keep Germany safe and voiced fears of more "ticking time bombs" among rejected asylum seekers who are yet to be deported.
He has vowed, if elected, to permanently lock down German borders with police controls on day one of his government, drawing comparisons to the rhetoric of US President Donald Trump.
His intent to push through the motions, and legislation on Friday, with AfD backing if needed sparked a jubilant response from the anti-immigration party, now polling above 20 percent.
"The firewall has fallen," wrote its top candidate Alice Weidel on X, the social media platform of tech tycoon and Trump ally Elon Musk, who has strongly backed her party.
In Germany, tens of thousands of protesters last weekend took to the streets with banners saying "Nazis out".
If Merz's push fails, the Bild newspaper wrote, it would also spell "pure election campaign support for the AfD" and Weidel "could put the champagne on ice".
"Nothing has made the right-wing populists bigger than the inability of the established parties to act on the issue of migration," Bild said.
© Agence France-Presse
