German Chancellor Angela Merkel's hardline interior minister Horst Seehofer is unhappy with an EU-wide deal she struck last week to reduce migration, sources said on Sunday, sharpening a crisis that threatens to bring down her conservative alliance.
After his Bavarian Christian Social Union (CSU) party spent weeks pressuring Mrs Merkel to toughen immigration and asylum policy, Mr Seehofer complained to allies that he had endured a "conversation with no effect" with the chancellor on Saturday, the sources said.
CSU leaders gathered in Munich from 3pm to decide their response to the EU deal, while Mrs Merkel and her lieutenants were to meet later on Sunday in Berlin.
European leaders agreed on Friday to new measures to reduce immigration into the bloc and so-called "secondary migration" of asylum seekers between countries.
Mrs Merkel, who has been in office since 2005, warned ahead of the summit that the issue of migration could decide the very future of the EU itself.
Earlier on Sunday, she told broadcaster ZDF she would do "everything possible to achieve results that mean we can continue to assume responsibility for our country", adding that "everyone knows the situation is serious" between her centre-right Christian Democractic Union and the CSU allies.
Mr Seehofer, who is CSU leader as well as federal interior minister, rejected her assessment that the EU-wide measures would "have the same effect" as his demand to turn away at the border asylum seekers already registered in other EU nations.
If he orders border police to go ahead with the scheme in defiance of the chancellor, Mrs Merkel would be forced to fire him, in turn prompting a CSU walkout that could cost her her majority in parliament.
The Bavarian party's discontent comes despite many of its long-standing migration demands appearing in the EU summit deal.
Leaders agreed on Friday to consider setting up "disembarkation platforms" outside the EU, most likely in North Africa, in a bid to discourage migrants and refugees boarding EU-bound smuggler boats.
Member countries could also create processing centres to determine whether the new arrivals are returned home as economic migrants or admitted as refugees in willing states.
At the national level, Mrs Merkel also proposes that migrants arriving in Germany who first registered in another EU country should be placed in "admissions centres" under restrictive conditions, according to a document she sent to the CSU and coalition partners the Social Democratic Party.
The document also outlined deals with 16 other countries to return already-registered migrants if they reached Germany.
The chancellor's frantic last-minute diplomacy was prompted by the CSU's fear of losing its absolute majority in Bavaria's state parliament, for which elections will be held in October.
But the CSU and CDU together form a centre-right force that has dominated German politics for decades.
Political stability was upset by Mrs Merkel's 2015 decision to keep borders open to migrants and refugees arriving from the Middle East via the Balkans, Hungary and Austria.
Since then, more than one million people have arrived in Germany, while Mrs Merkel's governments have repeatedly tightened immigration and asylum laws.
Nevertheless, the anti-refugee, anti-Islam Alternative for Germany (AfD) was propelled into federal parliament for the first time last year by outrage over immigration, leading to months of paralysis while Mrs Merkel struggled to find a workable coalition.
Opinion polls point to the AfD making a similarly spectacular entrance to Bavaria's parliament in October.
Weeks of "Merkel-bashing", however, have failed to help the CSU, as a Forsa poll last week showed up to 68 per cent of Bavarians backed Mrs Merkel's quest for a Europe-wide answer to migration rather than Germany going it alone.