European investigators have grilled Lebanon's finance minister as part of a probe into the wealth of the country's central bank chief, his former boss, a judicial official told AFP.

Youssef Khalil is a former central bank official who worked under Riad Salameh for almost three decades.

The caretaker minister answered "more than 100 questions" in three hours said the official, speaking on condition of anonymity because he is not allowed to speak to the press.

"Khalil answered the questions and said all transactions that took place at the central bank during his tenure were legal," he said, as the investigators wrapped up a two-week visit.

Salameh, 72, is part of Lebanon's political class widely blamed for a crushing economic crisis that began in late 2019 and which the World Bank has dubbed one of the worst in recent history.

The European investigators from France, Luxembourg, Belgium and Germany are looking into allegations of financial misconduct, including possible money laundering and embezzlement.

Salameh faces such allegations in separate probes in Lebanon and abroad, with investigators examining the fortune he has amassed during three decades in the job.

For procedural reasons, the delegation submitted questions to a Lebanese judge, who put them to Khalil in their presence, a judicial source previously told AFP.

They questioned him about topics including Forry Associates Ltd, a British Virgin Islands-registered company listing Salameh's brother Raja as its beneficiary.

Forry is suspected of brokering Lebanese treasury bonds and Eurobonds for a commission, which is then allegedly transferred to bank accounts abroad.

Khalil denied knowing "how to buy Eurobonds, or holding information about Forry's accounts," the official said.

The delegation questioned Salameh's brother Raja in Beirut on Thursday, after he had failed to appear three times.

They asked him 140 questions over six hours, mostly about his personal bank accounts and those of Forry.

Riad Salameh denied any central bank funds had gone to the company.

On Thursday, the investigators also quizzed Nada Makhlouf, an employee of Deloitte which has audited the central bank's finances since 1994.

In March 2022, France, Germany and Luxembourg seized assets worth 120 million euros ($130 million) in a move linked to a French probe into Riad Salameh's wealth.

In February, Lebanon charged Salameh with embezzlement, money laundering and tax evasion as part of its own investigation.

The domestic probe was opened following a request for assistance from Switzerland's public prosecutor looking into more than $300 million in fund movements by the Salameh brothers.

In March, European investigators questioned Lebanon's central bank chief, who denies wrongdoing and whose tenure ends in July, in Beirut.

He has also been summoned for a hearing in France on May 16.