Stop it! | Tobias Schwarz/AFP via Getty Images Gabriel to Merkel, Seehofer: Stop fighting! German vice chancellor says center-right row is destabilizing government.

The infighting on migration between center-right leaders Angela Merkel and Horst Seehofer is damaging the German government, Vice Chancellor Sigmar Gabriel has warned.

“Given the great challenge to our country because of the strong influx of refugees, the dispute between the CDU and CSU is threatening the government’s capacity,” Gabriel, leader of the Social Democrats, the junior coalition partner, told Spiegel online Friday. "This form of mutual blackmail and insult is unworthy and simply irresponsible."

The past week has seen increasing tensions between Chancellor Merkel, leader of the Christian Democratic Union (CDU), and its Bavarian sister party the Christian Social Union (CSU), led by Seehofer.

On Tuesday, Seehofer blasted Merkel's "open border" policy and gave her an ultimatum: Change your policy on migration or else. He gave the chancellor until Sunday to change tack, but did not say what would happen if she failed to comply.

Merkel and Seehofer are scheduled to hold one-on-one talks on Saturday, with Gabriel joining them on Sunday evening to discuss the migration crisis.

Gabriel warned that “the longer the dispute in the union lasts, more people will turn away from politics and right-wing extremists will gain more ground.”

Another senior Social Democrat, party general-secretary Yasmin Fahimi, criticized Seehofer's behavior, saying that the CSU’s demands were not helpful.

“The country needs a stable government, the CSU must stop to behave like a child,” she told television station ZDF.