Taha al-Jumailly, 27, also stands accused of crimes against humanity, war crimes and human trafficking in the case which is being heard before judges in Frankfurt.

Wearing a white shirt in court, he gave no initial response after being formally advised of the charges against him.

Jumailly's wife, a German woman named Jennifer Wenisch, has been on trial for a year at a Munich court.

She too is charged with murdering the young Yazidi girl who the pair are believed to have allowed to die of thirst in the Iraqi city of Fallujah in 2015.

The start of Wenisch's trial in April last year appeared to be the first formal proceeding anywhere in the world related to the Islamic State group's persecution of the Yazidi community.

A Kurdish-speaking group hailing from northern Iraq, the Yazidis were specifically targeted and oppressed by the jihadists beginning in 2015.

The mother of the young girl, identified only by her first name Nora, has repeatedly testified in Munich about the torment visited on her child, named as Rania.

Court documents allege that Jumailly joined IS in March 2013, holding different positions within its hierarchy in the jihadists' "capital" in the Syrian city of Raqa, as well as in Iraq and Turkey.

- 'Regularly beaten' -

German prosecutors say the accused bought a woman belonging to the Yazidi minority and her five-year-old daughter as slaves at the end of May or beginning of June 2015.

He then took them to Fallujah, where they were seriously maltreated and at times deprived of food, the prosecutors allege.

"They were not allowed to leave the house unaccompanied. He forced them to wear a full veil, and did not accept the child's name because it was a name of the infidel," chief prosecutor Anna Zadeck said Friday.

"Both were regularly beaten. The woman has suffered pain in her shoulder ever since. The child once had to stay in bed for four days after being beaten."

In the summer of 2015, after a string of such abuses, the young girl was chained by Jumailly to the window of a house where she lived with her mother, as "punishment" for having wet the bed, prosecutors said.

She died of thirst in temperatures as high as 50 degrees Celsius (122 Fahrenheit).

The couple also forced her mother to walk barefoot on the scorching ground outside, inflicting severe burns, the prosecution claims.

Mother and daughter had been kidnapped in the summer of 2014 after the IS group invaded the Sinjar region of Iraq.

They were repeatedly sold on "slave markets", prosecutors say.

The Frankfurt case is expected to last until at least August, and is being heard under tight police guard.

Jumailly was arrested in Greece in May 2019, before being extradited to Germany in October, where he has since been held in pre-trial custody.

- 'No order to exterminate' -

Both Lebanese-British lawyer Amal Clooney and Yazidi activist Nadia Murad -- herself a survivor of IS sexual slavery and a 2018 Nobel Peace Prize winner -- have represented the mother of the young girl at Wenisch's trial.

The two women lead an international campaign to classify IS crimes against the Yazidi community as genocide.

But proving before a court that genocide has taken place is difficult.

The explicit will to destroy a group such as the Yazidi must be demonstrated to judges' satisfaction.

"There is often no order to wipe out" a group, University of Leipzig legal expert Alexander Schwarz told AFP.

"There are no written instructions where 'exterminate the Yazidi' appears."

The small ethnic and religious minority is believed to have been most ferociously persecuted by the jihadists, who forced their women into sexual slavery, recruited the underage as child soldiers and murdered hundreds of men.

In August 2014, the killings of 1,280 Yazidi and kidnappings of 6,400 more may have constituted a genocide according to the UN.

Non-Arab, non-Muslim Iraqis, many Yazidi have fled to Germany.

Murad, a Nobel Peace Prize winner, is among those to have passed through a programme there for women and children -- many victims of repeated rapes -- since its inception in 2014.