A German soldier who posed as a Syrian refugee denied plotting an attack on high-ranking politicians as he went on trial in Frankfurt on Thursday in a bizarre case fuelling concerns over right-wing extremism.

Franco Albrecht, 32, stands accused of plotting "a serious act of violence that endangers the state". He is also charged with fraud and illegally possessing weapons and explosives.

His lawyer told the court that Albrecht was the victim of a "public witch hunt" and "character assassination", and denied his client had planned an attack.

Yet prosecutors say the Bundeswehr lieutenant had taken weapons and explosives from the German army in his plot to carry out an attack on targets including high-ranking politicians such as then justice minister Heiko Maas.

Despite speaking no Arabic, he had also successfully posed as a Syrian refugee in order to "redirect suspicion onto asylum seekers in Germany in the subsequent investigations" of the attack, they said.

Arrested in 2017 while trying to retrieve a Nazi-era pistol he had hidden in a toilet at Vienna's international airport, Albrecht rejected the allegations.

If convicted in the trial set to last until August, he could face up to 10 years in prison.

The trial's opening has already been delayed several times by questions over which court was competent to hear the case.

Prosecutors claim Albrecht, the son of a German mother and an estranged Italian immigrant father, harboured "right-wing extremist views", including a particular antipathy towards Jewish people.

According to a court document from 2019, investigations showed he owned a copy of Adolf Hitler's book "Mein Kampf" and believed immigration to be a form of genocide.

Albrecht's lawyer told the court that his client was not a right-wing extremist, and said he had posed as a refugee "in order to highlight security gaps in the (immigration) system".

Using makeup to darken his face and pretending to be a Christian fruit seller from Damascus, Albrecht successfully applied for asylum in his own country under the name "David Benjamin".

Franco Albrecht, 32, stands accused of plotting "a serious act of violence that endangers the state". He is also charged with fraud and illegally possessing weapons and explosives
Franco Albrecht, 32, stands accused of plotting "a serious act of violence that endangers the state". He is also charged with fraud and illegally possessing weapons and explosives POOL / Boris Roessler

Despite speaking no Arabic, he obtained a space in a shelter and monthly benefits of 409 euros ($485), before later returning to his barracks in Illkirch on the French border.

His double identity was uncovered only upon his arrest in 2017, when police found that his fingerprints produced two separate matches.

The fraud laid bare the struggles of Germany's immigration system to cope with the influx of more than one million asylum seekers -- many of them Syrian -- during the refugee crisis of 2015 and 2016.

"I tried to be prepared the best I could," Albrecht said of his scheme in an interview with The New York Times published in December. "But in the end, it was not necessary at all."

In a recent interview with French daily Le Figaro, he said he knew what he was doing was against the law.

Yet he claimed he had procured the weapons only "to protect his family in case of an emergency".

Prosecutors, however, say that he planned to use both the pistol and other weapons and explosives in order to carry out an attack under his false refugee identity.

They believe that the targets were Maas, the then justice minister, deputy speaker of parliament Claudia Roth or a human rights activist.

The revelations strained the relationship between the armed forces and the defence minister at that time, Ursula Von Der Leyen, who is now president of the European Commission.

It also raised questions over the army's seriousness about combating right-wing extremism within its ranks.

Von der Leyen's successor Annegret Kramp-Karrenbauer ordered the partial dissolution of the KSK commando force last year after revelations that some of its members harboured neo-Nazi sympathies.

Following a string of far-right terrorist attacks over the last two years, Interior Minister Horst Seehofer has declared right-wing extremism the "biggest security threat facing Germany".

He has promised tougher security measures, including a crackdown on online hate speech.