This week’s terror arrests in Germany are a direct result of Angela Merkel’s decision to open the borders to over a million migrants last year, the Bavarian Interior Minister has said.

Joachim Herrmann, who is a member of the Christian Social Union (CSU) , said the fact Germany had to arrest suspected terrorists was “revenge” for failing to control immigration, and that Germany was “reaping the harvest” of the policy.

“Thousands of people came to Germany without adequately verified identities,” he said.

“We now know that ISIS purposefully took advantage of these vulnerabilities to camouflage assassins as refugees.”

Mr Herrmann’s intervention represents a deepening of tensions between the CSU and Angela Merkel’s Christian Democratic Union (CDU), with whom they have been in a permanent electoral alliance since the end of the Second World War.

According to Frankfurter Allgemeine Zeitung, the minister added: “We need strict border controls and clear identification of who is coming into our country.”

“People whose identities cannot be made certain without any doubt must be held at the border, pending clarification.”

The CSU has been consistently critical of Angela Merkel’s border policies since the start of the migrant crisis, adopting tough border controls in Bavaria against the wishes of Federal German politicians.

Two weeks ago, Bavaria’s Finance Minister Markus Söder, another CSU member, said Germany should aim to send a large number of the migrants home as integrating so many people would be impossible.

“Even with the best intentions, it will not work to integrate successfully that many people from a completely foreign culture,” he said.

“Germans do not want a multicultural society. Anyone who wants to live here must adapt to our values and not vice-versa.”

The huge influx of migrants has also led to a rise in popularity for the anti-mass immigration Alternative for Germany (AfD) party, which inflicted a humiliating defeat on Angela Merkel’s party in her home state earlier this month.

The insurgent party came from nowhere to take 20 per cent of the vote in Mecklenberg-Vorpommen, forcing the CDU into third place on 19 per cent.

The success of the party has inspired the Bavarian CSU to take an increasingly hard line on immigration.

Earlier this month, they called for authorities to prioritise Christian migrants when deciding who should come into Britain in a policy paper titled “Germany should remain German”.

Germany is scheduled to go to the polls in federal elections next year.