NEW YORK (AFP) - JPMorgan Chase said Thursday that it was cooperating with law-enforcement officials to determine the scale of reported cyber attacks against US financial institutions.
The largest US bank by assets said it was not seeing any sign of unusual fraud activity.
Late Wednesday, the Federal Bureau of Investigation (FBI) said it was "working with the United States Secret Service to determine the scope of recently reported cyber attacks against several American financial institutions."
According to people close to the situation, there has been no sign of hacking at three big New York banks, Goldman Sachs, Citigroup and Morgan Stanley.
The FBI declined to provide other details, but US media are reporting between two and five banks may have been targeted in coordinated cyber attacks that allowed hackers to steal several gigabytes of sensitive data.
Bloomberg news agency, citing sources close to the investigation, reported that hackers broke into the computer systems of JPMorgan Chase and a second US bank earlier this month.
The sophistication of the attack suggested it could be organised by a government. Bloomberg said two people familiar with the probe confirmed that the FBI was examining the case to see if it is retaliation for US sanctions against Moscow over its support of Ukraine's secessionist rebels.
Some major US companies have been the victims of large cyber attacks in recent months, but in many cases the hackers were suspected of being based in China.
A JPMorgan spokeswoman said Wednesday that "companies of our size unfortunately experience cyber attacks nearly every day."
"We have multiple layers of defence to counteract any threats and constantly monitor fraud levels."