Germany’s interior minister dramatically announced plans to resign on Sunday night, after a heated showdown with chancellor Angela Merkel over migration. Horst Seehofer, Germany’s Interior Minister and leader of the Christian Social Union (CSU), said on Sunday evening that he wanted to resign from all offices, after hours of heated talks with his party. Mr Seehofer said the conflict with Mrs Merkel over migration was affecting the “credibility” of his role as party leader. He also slammed the migration deal Mrs Merkel secured with her EU counterparts last week as “ineffective”. Mr Seehofer has been a fierce critic of Mrs Merkel and in particular her decision to open Germany’s doors to over 1 million migrants in 2015. With that in mind his resignation may be welcome news to the chancellor. However it is yet to be seen who his replacement would be and many in his party share his tough stance on immigration. Two weeks ago Mr Seehofer gave Mrs Merkel an ultimatum to find a European solution to irregular migration by this Sunday, or he would defy her by turning migrants back at the border against her wishes. Merkel's migration tensions | Read more After a two-day summit with EU leaders in Brussels last week, Mrs Merkel believed she had struck such a deal. However, Mr Seehofer apparently does not agree. After an “ineffective” two-hour meeting on Saturday night between Mrs Merkel and Mr Seehofer, the two leaders met with their respective parties for separate meetings in Munich and Berlin on Sunday night. During the talks, Mr Seehofer reportedly considered three options: compromise with the chancellor’s Christian Democrats (CDU), remain firm on his threat to defy her and risk the breakup of the union, or resign. According to information from the German press agency, Mrs Merkel has spoken to her executive committee of a “very serious” situation. Mrs Merkel on Sunday afternoon firmly reiterated her desire for a solution that is “not unilateral” and ”not to the detriment of third parties,” in an interview with German ZDF television. CDU Secretary General Annegrete Annegret Kramp-Karrenbauer, Angela Merkel and minister Julia Kloeckner met on Sunday Credit: Michele Tantussi/Getty Images However she also said on her way into the discussions with her party in Berlin on Sunday afternoon that she had taken the CSU’s issue into account. “I want the CDU and CSU to work together, because we are a success story for our country,” she said. Tensions were high in Berlin on Sunday as party talks ran into the night. Michael Theurer, of the Free Democratic Party (FDP) said: “The mutual trust of CDU and CSU is more or less destroyed… and the government chaos produced harms Germany and its citizens.” However the effectiveness of the migration deal struck by Mrs Merkel and other EU leaders this week was also questioned. Mrs Merkel circulated a document to her coalition partners after the summit saying that 14 countries had agreed “on a political level” to take back some migrants who had passed through other EU countries on their way to Germany. But the Czech Republic, Poland and Hungary later said they had not signed the agreement. A protestor holds a placard reading “Merkel must go” outside the CDU headquarters Credit: REUTERS/Axel Schmidt Leaders agreed to set up “voluntary” control centres within the EU to process migrants. However Austria, France, Germany and Italy did not commit to any immediate plans to open secure centres on their own soil. Following the summit Mrs Merkel admitted there was still “a lot of work to do to bridge the different views”. Donald Tusk, the European Council president, said it was a “sort of” political breakthrough, but also added it was “too early” to call it a success. However Emmanuel Macron, the French President, hailed the agreement as an example of “European cooperation”. Germany’s coalition government has been plagued by tensions since it was formed in February, four months after the German federal election last November. Mr Seehofer blamed his party losing seats to the far-Right Alternative for Germany (AfD) during the last election on Mrs Merkel’s open-door refugee policy. With the Bavarian state elections due in October, Mr Seehofer had feared the CSU could now lose its outright majority to the AfD. He has previously reportedly said of Mrs Merkel “I cannot work with this woman anymore”.