German doctors have criticised a proposal to impose mandatory age checks on young asylum seekers who claim to be under 18.

The German Medial Association said the tests are unethical and 'an invasion of personal well-being', local media reports.

The critique comes after a young asylum seeker stabbed a teenage girl to death. His age has now been questioned.

Killer: The proposal of mandatory age checks comes after Afghan asylum seeker Abdul Mobin D., right, who claims to be 15 years old, was arrested in Kandel, south-west Germany, accused of stabbing his ex-girlfriend, Mia V., 15, left, to death

The proposal has come from the Christian Social Union (CSU), the sister party of Chancellor Angela Merkel's Christian Democratic Union (CDU), which has three ministers in the German cabinet.

CSU MPs want to enforce medical exams, such as x-rays, to test age of all asylum seekers who claim to be under 18, The Local reports.

This comes just days after a 15-year-old German girl only identified as Mia V. was stabbed to death in Kandel, a town in the south-western German state of Rhineland-Palatinate.

The alleged killer has been named in German media as Abdul Mobin D., an asylum seeker from Afghanistan who was Mia V's ex-boyfriend.

He reportedly attacked her with an 8-inch kitchen knife after following her to a chemists on December 27.

Victim: Mia V. was stabbed to death outside this chemist's in Kandel, just weeks after she had broken up with her 'mean and jealous' boyfriend

The attacker was overpowered by witnesses who restrained him until police officers arrived.

Abdul Mobin D. arrived in the German state of Hesse in April 2016 as an unaccompanied refugee, telling the authorities he was 15 years old.

Abdul Mobin D. and Mia V. had reportedly had a relationship which lasted several months, but that she broke up with him early December after he became 'jealous and mean'.

The victim's father David V. said he and his family initially welcomed Abdul Mobin D. 'like a son' as 'otherwise he would have had nobody', but adds that he always doubted his age.

'He is never in a million years 15-years-old. We hope that through the procedure [age test] that we will now know his true age.'

Following the end of the relationship, Abdul Mobin D. reportedly stalked and threatened Mia V. This saw her parents file a complaint, accusing the Afghan national of insults, threats and coercion.

Police officers had notified the asylum seeker of proceedings in person on the morning of the fatal stabbing.

Abdul Mobin D. remains in police custody but has so far refused to speak to authorities.