PARIS, France: Hackers stole approximately €100 million ($112.61 million) from French banking group Credit Mutuel Arkea in an unusual cyber heist targeting a mainstream financial institution, prompting a criminal investigation and the temporary suspension of some banking transactions.

The lender confirmed on November 5 that it was working to recover the stolen funds but could not yet determine how much money would be retrieved.

The attack, first disclosed on November 4, follows a $6.3 billion cryptocurrency theft from Binance last week and a series of cyberattacks targeting internet-connected refrigeration systems across Europe.

According to Credit Mutuel Arkea, the attackers used an account belonging to the bank to carry out "fraudulent transactions".

The stolen funds were not held in cryptocurrency, although the bank said they could have been converted into digital assets after the theft.

As a precaution, Credit Mutuel Arkea temporarily suspended certain transactions, causing delays to some transfers. However, the lender said customer assets had not been affected.

A spokesperson also rejected media reports suggesting that Fortuneo, the group's online banking subsidiary, had been used as the entry point for the attack. The spokesperson said neither Fortuneo nor its customers' accounts were involved.

Cybersecurity specialists told Reuters that although attacks against financial institutions are common, successful virtual thefts of money from conventional banks remain unusual.

Rafay Baloch, chief executive of cybersecurity and security engineering company RedSecLabs, described the incident as unprecedented in Europe.

"We're seeing a lot of these sophisticated attacks targeted at the application layer and sophisticated social engineering attacks being targeted at banking institutions," he said.

The Paris prosecutor's office confirmed that its cybercrime unit received a complaint from Credit Mutuel Arkea on November 4 and immediately launched an investigation led by France's cybercrime police.

The bank said it had informed the European Central Bank, French banking supervisors and prosecutors about the incident.

Its spokesperson declined to identify the third-party service provider whose platform was used in the attack. France's banking regulator, the ACPR, declined to comment.

Financial regulators worldwide have increasingly warned about cybersecurity threats to banking institutions, particularly as artificial intelligence technology develops.

"Any time you have a hit in the financial system, it's a big deal," said Puneet Kakkar, managing director at Nardello & Co in Paris.

Credit Mutuel Arkea, based in Brittany, is a French cooperative banking group serving more than 5.8 million customers and holding €211.5 billion in assets.

It belongs to the wider Credit Mutuel banking network and is affiliated with its central body while retaining considerable strategic independence.

Kakkar said French banks generally maintain strong cybersecurity standards because of regulatory requirements. Nevertheless, he warned that "cybercriminals are becoming more opportunistic and more creative".

Previous major banking cyber thefts include the 2016 attack in which hackers stole $81 million from the Bangladesh central bank's account at the Federal Reserve Bank of New York.