BERLIN, June 21 (Xinhua) -- The German Social Democrats (SPD) have lashed out at their Christian Democratic Union (CDU) and Christian Social Union (CSU) coalition partners on Thursday for hampering the work of the government with their infighting over asylum policy.

Speaking to the public radio station Bayerischer Rundfunk 2, SPD secretary general Lars Klingenbeil complained that Chancellor Angela Merkel's (CDU) cabinet was "unable to implement the coalition agreement" due to the escalating CDU-CSU dispute.

Klingenbeil called for a swift resolution of the internal conflict which was perceived as an unnecessary nuisance by many Germans.

The CDU and CSU have reached a political impasse over the question of whether or not to turn back asylum seekers at the German border who were already registered in another Schengen area country.

As outlined in his "migration master plan", interior minister and CSU leader Horst Seehofer wants to refuse asylum access to German territory if they have already formally entered the Schengen zone via another country.

By contrast, CDU leader Merkel has warned of a resulting domino effect as Germany's neighbors rush to shutter their internal Schengen borders and is calling for a joint European solution to the "refugee crisis".

The veteran stateswoman is under pressure to find such an alternative ahead of an upcoming EU summit in only two weeks before the CSU has threatened to press ahead with its own plans without obtaining her consent.

While the interior minister can technically enact some policies related to immigration and asylum without the chancellor's consent, such a move would mark an unprecedented show of disobedience within a German government.

Merkel could in turn respond by stripping Seehofer of his cabinet position, raising the specter of a violent unraveling of the ruling grand coalition.

First voices of resignation are heard inside Merkel's party, as German newspaper Augsburger Allgemeine reported that CSU politician and Bavarian finance minister Pschierer urged Merkel to resign at a campaign event.

Pschierer subsequently doubled-down on his statement when questioned by press, arguing that the chancellor was already "past the peak" of her political career.

Germany's Social Democrats argue that the dispute between the CDU and CSU demonstrated that the SPD's decision to enter the Merkel's fourth governing cabinet was right.

A social-democratic voice of reason was urgently needed in light of the CSU's persistent attempts to drag Germany to the "right-wing spectrum of politics" and "cause division in Europe", says SPD secretary general Klingenbeil.