German authorities are yet to approve the extradtion of the ex-deputy, wanted on embezzlement charges.

German law enforcers on November 29 detained former MP Oleksandr Onyshchenko in the German city of Aachen at the request of the National Anti-corruption Bureau of Ukraine and the Specialized Anti-corruption Prosecutor's Office.

Journalists of the Skhemy investigative project learned about this from two independent sources in various law enforcement agencies.

According to the procedure, the German court must next decide on his further extradition to Ukraine, which was requested by Ukrainian law enforcement authorities.

The court must also determine a preventive measure pending consideration of the issue.

The date of the hearing is yet to be announced.

Read alsoUkraine's high profile "Gas case": Indictment forwarded to court

Ahead of the trial, Onyshchenko is being held in custody, the report says.

Onyshchenko's lawyer, Oleh Ishchenko, in a comment to Skhemy, said he was not ready to comment on the report about his client's detention.

NABU detectives in December 2015 began a pre-trial investigation of the theft of funds during the extraction and sale of gas under Ukrgazdobuvannia's joint ventures, as a result of which the state suffered losses amounting to about UAH 3 billion.

The investigation established that from January 2013 to June 2016, the suspects illegally seized UAH 1.6 billion, received from gas sales, inflicting damage to Ukrgazvydobuvannya in the amount of over UAH 740 million. Detectives found that 29 persons had been involved in the commission of crimes. Seven of them, in particular, the organizer of the scheme, MP Oleksandr Onyshchenko, have been put on wanted list.

The Verkhovna Rada deprived Onyshchenko of parliamentary immunity, and also voted for his detention and arrest. But before that, using parliamentary immunity, he fled from Ukraine.

On November 14, NABU chief Artem Sytnyk said Onyshchenko could be extradited from Spain to Ukraine as early as this December.