Friedrich Merz was speaking at his opposition Christian Democratic Union's (CDU) congress after the revelation that members of the hard-right Values Union group last year discussed plans to deport "unassimilated" citizens at a retreat with far-right influencers and Alternative for Germany (AfD) politicians.

Rising prices, the economic shock caused by Russia's invasion of Ukraine, and the burden placed on public services by high immigration have contributed to a sullen mood in Germany that is punishing all the mainstream parties.

"At the next party congress I will bring a motion making Values Union membership incompatible with CDU membership," Merz said on Saturday, in his first comments on November's meeting at a villa outside Berlin.

After a period in which the CDU has been among the most hawkish voices on immigration in German politics, Merz used a news conference to emphasise his party's distance on that - and other issues - from the AfD.

The CDU is on around 30% in the polls - a historically low level for the party - around twice the level of Chancellor Olaf Scholz's Social Democrats and his Green coalition partners, with the AfD snapping at Merz's heels on as much as 24%.

"Germany has been a country of immigration for decades," he said. "One that very successfully integrated immigrants".

The balancing act was still present, however, as he warned that some groups, "often but not always of Islamic faith", were less well integrated.

All mainstream parties have been criticised for focusing on the AfD's themes, promising to deal more toughly with illegal immigration despite warnings from experts that this only legitimises the insurgent far-right's discourse.

The congress is being held to adopt a new fundamental programme that Merz bills as a return to clear-cut conservatism after the long years of centrism under four-term Chancellor Angela Merkel.

The new programme, the fourth in the CDU's history, strikes populist notes on immigration, pledging to keep asylum applicants outside the European Union while their applications are assessed.

"We are going to target the AfD," Merz said. "On their Europe policy, on their foreign policy and their ties to Russia. And especially on their economic policy ... Many entrepreneurs have sympathies for the AfD."

(Reporting by Andreas RinkeWriting by Thomas EscrittEditing by Mark Potter)

By Andreas Rinke and Thomas Escritt