BERLIN, July 11 (Xinhua) -- Former German chancellor Gerhard Schroeder (SPD) has criticized the incumbent Chancellor Angela Merkel (CDU) on Wednesday for failing to keep rebellious ministers in her ruling "grand coalition' in check.

Speaking to the magazine "STERN", Schroeder argued that the chancellor of Germany could never allow subordinate cabinet members to issue an ultimatum to the head of the government. He hereby referred to the recent escalation of a cabinet row over asylum policy in which interior minister Horst Seehofer (CSU) threatened to resign from his post unless Merkel backed his controversial "migration master plan".

The former chancellor argued that there were only two means of addressing a cabinet conflict in which differences of opinion could not be resolved. Schroeder said that the chancellor should "either force the opponent into solidarity by asking for a vote of confidence on the issue in question, or sack the minister".

In the event, Merkel's Christian Democratic Union (CDU) and Seehofer's Christian Social Union (CSU) eventually reached a compromise to detain asylum seekers already registered in the EU in so-called "transit-centers" at the German-Austrian border before arranging their transfer to another responsible European Union (EU) member state. Both parties vowed to maintain a spirit of European solidarity and seek to cooperate closely with neighboring states in implementing the still-vaguely defined new policy proposal.

However, Seehofer subsequently reiterated his desire to achieve an "urgently needed U-turn on asylum' by establishing a stricter national policy regime in Germany at the long-awaited presentation of his "migration master plan" on Tuesday.

Commenting on the development in "STERN", Schroeder warned that the CSU's apparent attempt to contain the rise of the Alternative for Germany (AfD) by toughening its own rhetoric on immigration would prove a "fatal mistake" for the party.

According to Schroeder, resulting infighting in the federal government had "harmed Germany" and undermined the authority of its government. "Some in Europe who do not appreciate Germany's role on the continent will secretly be delighted," he said.

While blaming the CSU for "organizing instability" and chancellor Merkel for not imposing her will in response, Schroeder also attacked the German Social Democrats (SPD) for tolerating Seehofer's unusual antics instead of demanding a vote of confidence. The SPD was largely absent in asylum related quarrels between the CDU and CSU and it still remains unclear whether it will lend its necessary support to the compromise achieved between the two conservative sister parties.

A recent "Insa" opinion poll in Germany showed that the AfD (16 percent) has overtaken the SPD (15.5 percent) for the first time ever in a national survey of voter sentiment. A separate "Deutschlandtrend" poll found that Seehofer's approval rate collapsed by 16 percentage points to the lowest ever level of 27 percent in July, while Merkel's approval rating fell by a relatively modest two percentage points to 48 percent during the same period.