By Erik Kirschbaum
BERLIN (Reuters) - The leader of Germany's Christian Social Union told Chancellor Angela Merkel on Friday that he would not join forces with her Christian Democrats - the CSU's coalition allies - at a key party congress unless she changed her open-door refugee policy.
In a fresh attack on the chancellor's pro-refugee policies that have cost the sister parties support, Bavaria state premier Horst Seehofer said her refusal to change course was only helping the far-right Alternative for Germany (AfD).
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He threatened to skip the CDU's annual party congress in December - an unprecedented blow to the usual unity of the conservative bloc nine months before next September's election.
"It doesn't do any good for people to keep saying 'We've done everything right, you just don't understand it'," Seehofer said, a direct rebuttal of Merkel's fiery defense of her pro-refugee policies in parliament on Thursday.
"That's only going to make the AfD stronger," he told Der Spiegel magazine ahead of a two-day meeting of CSU leaders to Saturday. Nerves in the CDU/CSU are on edge after the CDU suffered a historic defeat last Sunday, falling to third place behind even the AfD in the state of Mecklenburg-Vorpommern.
Even though Merkel's CDU and Seehofer's CSU are sister parties linked as a single conservative bloc in parliament, the CSU has firmly demanded that Merkel introduce upper limits on the number of refugees after more than one million arrived last year. Merkel has repeatedly refused any such limits.
"There can't be any compromise about that," Seehofer said, adding he would not make the customary guest visit for a speech to Merkel's CDU party congress in December if the two parties do not find common ground - tantamount to an insult to Merkel.
"Without reaching a consensus on that, my appearance (at the CDU congress) would be nothing more than a media spectacle," he said. But he added: "The CDU is not our political opponent."
Even though the CDU and CSU traditionally agree on a joint candidate for chancellor, Seehofer has not yet endorsed Merkel and Sunday's regional election defeat prompted speculation she may not stand for a fourth term. Her popularity has waned in the last year due to her handling of the migrant crisis.
The AfD has fed on fears about the influx of around a million migrants to Germany last year and siphoned voters from all parties. It is now represented in nine of Germany's 16 states and looks poised to enter the Bundestag next year.
Earlier on Friday, Seehofer's party ally Joachim Herrmann called for deportation of migrants denied asylum in Germany to crisis zones like Afghanistan and other measures, a further illustration of the widening rift between Merkel and the CSU.
Herrmann told Bild newspaper he advocated the repatriation of people from northern areas of Afghanistan and other crisis areas who had been denied asylum, something that Merkel's government has previously declined to do.
An opinion poll by the TNS institute for Der Spiegel found that 82 percent are opposed to Merkel's policies on refugees while 15 percent said she should stick to her guns.
"Right now we need clear, reliable rules for migrants," said Seehofer. "It's my deepest conviction (that we need limits) and it's also quite clearly what the public wants."
(Writing by Erik Kirschbaum; additional reporting by Andrea Shalal; Editing by Richard Balmforth)