Five days before the start of exploratory coalition talks, the CDU, CSU and SPD are in dispute over age checks on young refugees.

After a 15-year-old Afghan asylum seeker stabbed his teenage ex-girlfriend in the Rhineland town of Kandel, the prospective coalition parties have come down on opposite sides of an immigration debate.

There are significant doubts about the young asylum seeker’s age, including some who believe he may be 18 and liable to be tried as an adult. Child migrants also have a number of privileges over adults, including more comprehensive care from the state, and a deportation ban.

Currently it is up to youth welfare offices to determine the age of unaccompanied minors arriving in Germany.

Mrs Merkel’s CDU and its Bavarian sister party, the CSU, are in favour of mandatory medical checks on migrants’ ages, particularly in cases where there are significant doubts.

However, the left-wing SPD, which could continue its “grand coalition” with the CDU and CSU after the upcoming talks, argues the current legislation is enough. Led by former EU Parliament president Martin Schulz, the SPD is generally in favour of immigration and open borders.

The CSU’s recently announced intention to decrease migrant benefits is another matter of contention.

Asylum seekers are currently reimbursed only for basic needs for their first 15 months in Germany, before being entitled to more benefits. The CSU would extend this to 36 months, as well as further restricting benefits for immigrants whose asylum claims are rejected.

The head of the CSU group in the Bavarian parliament, Alexander Dobrint, told a Munich newspaper: “So that Germany is no longer a magnet for refugees from all over the world, we want to cut social benefits for asylum seekers.”

The CSU’s plans would also restrict benefits until the government could verify asylum claimants’ identities with complete certainty. Their draft resolution on the subject says: “When we take people in with us, we need to know who they are.”

This again puts Mrs Merkel’s “Union” parties in direct opposition to the SPD, which would not restrict benefits or introduce such rigorous testing.

It also represents a U-turn for the Chancellor, who had insisted Germany keep its borders open to refugees after spending her early years in East Germany, where travel was severely restricted.

However, her decision to allow around one million refugees into the country in 2015 backfired as voters turned on her.

The Chancellor was accused of being lax with national security as a wave of terrorist attacks unfolded in Europe.

Germany’s former intelligence chief has also urged Mrs Merkel to introduce further border controls, warning the country will face a significant security threat “as long as we let people come into the country without identity papers”.

August Hanning, who ran Germany’s Federal Intelligence Service (BND) from 1998-2005, criticised Angela Merkel’s refugee policy, claiming an undeniable “link between internal security and efficient border control”.