Maria Efimova – the Russian whistleblower at the centre of a corruption scandal involving Malta’s prime minister Joseph Muscat – is being held in jail in Athens, a press spokesman of the Hellenic Police said.

Speaking to The Shift News, the spokesperson said Efimova voluntarily gave herself in to the police in Athens on Monday night and she was arrested after the police confirmed that she has two pending arrest warrants issued by Malta.

Last year, Efimova testified in front of a magisterial inquiry into allegations that the Maltese Prime Minister Joseph Muscat’s wife was the owner of a Panama offshore company called Egrant Inc, which declaration of trust the whistleblower says she had seen while working at Pilatus Bank.

Efimova’s claims about Pilatus Bank were first reported by the journalist Daphne Caruana Galizia, who was killed by a car bomb on 16 October 2017.

In the run-up to last year’s general election, Caruana Galizia published Efimova’s account, which included details about an alleged $1 million transfer to Egrant from Azerbaijan’s ruling family. The allegations have been denied by Pilatus Bank and Muscat but a magisterial inquiry is still ongoing.

On Tuesday, the US Southern District Attorney’s office announced the indictment of Pilatus Bank owner Ali Sadr Hasheminejad, for money laundering.

Efimova, the Greek police spokesperson said, “is now being held in jail in Athens until the judicial authorities take a decision on whether to extradite her to Malta or not.”

Asked how long the process is expected to take, the Greek police spokesperson said this could take up to three months, but the timeframe depends on the court and on whether Efimova is willing to be extradited.

On Tuesday, Greek MEP Stelios Kouloglou told the Guardian “She (Efimova) called me last night from the police station. She told me she turned herself in because she was afraid. Her husband called this morning. He said she was terrorised and saying she was going to die.”

The Greek police spokesperson could not confirm this and said he had “no knowledge” of any particular threats received by Efimova.

In a statement, Kouloglou – who had been helping Efimova with an application for residency in Greece – said “The arrest warrant against Maria Efimova is based on ridiculous accusations by Malta’s authorities. Her possible extradition to Malta would seriously jeopardize her life. Greek Justice, that is investigating her case after she surrendered to the police, must take into serious consideration the murder of Daphne Caruana Galizia, to whom whistleblower Maria Efimova had given a lot of revealing information concerning financial scandals.”

Earlier, MEPs sitting on the ad-hoc Rule of Law Delegation to Malta, urged Greek authorities not to send Efimova back to Malta.

“Maria Efimova is a material witness in investigations on corruption and money laundering in Malta, involving Pilatus Bank and government members exposed by Panama Papers and Malta’s FIU.

“We call on the Greek authorities to provide Maria Efimova with protection and safeguard of her security and that of her family and to not return her to Malta,” the MEPs added.

Efimova absconded from Malta after saying that she feared for her life and that of her family, including her elderly father in Moscow who she said was being intimidated by “dodgy people.”

Malta issued an international arrest warrant after Efimova failed to attend court hearings into a criminal complaint filed against her by her former employer Pilatus Bank.

The woman is the subject of two criminal proceedings. She is accused of defrauding Pilatus Bank of some €2,000 and of having made false accusations against Superintendent Denis Theuma and inspectors Jonathan Ferris and Lara Butters.

In January, Cyprus also issued an arrest warrant which Efimova said was part of a plot to have her extradited to Malta.