JPMorgan Chase & Co is investigating a possible cyber attack and working with law enforcement authorities to determine the scope, a company spokeswoman said on Thursday morning.

The bank was taking additional steps to safeguard sensitive or confidential information, though it did not see unusual fraud activity at this time, company spokeswoman Trish Wexler said.

JPMorgan disclosed the investigation after the FBI said Wednesday evening it was investigating media reports earlier in the day that several US financial companies have been victims of recent cyber attacks.

"We are working with the United States Secret Service to determine the scope of recently reported cyber attacks against several American financial institutions," FBI spokesman Joshua Campbell said in a statement late Wednesday.

Campbell did not name any companies or give more details, although media reports had named JPMorgan as one victim of the attacks. Other potential victims have yet to be named.

Officials with the Secret Service could not be reached for comment.

JPMorgan launched its investigation after malicious software was recently discovered in the bank's network, signaling it was the victim of a cyber attack, two people familiar with the incident told Reuters. The bank has yet to determine the severity, said the sources, who asked not to be identified because they were not authorized to speak publicly about the matter.

Bloomberg News reported Wednesday that Russian hackers were believed to have carried out cyber attacks against JPMorgan and another unnamed U.S. bank in mid-August, resulting in the loss of sensitive data. Authorities were investigating whether the breaches were linked to recent attacks on major European banks, Bloomberg reported.

The New York Times reported late Wednesday the networks of JPMorgan and at least four other U.S. banks had been infiltrated in a string of coordinated attacks this month, citing four people familiar with the investigation.

The attackers stole large quantities of data, including checking and savings account information, though their motivation was not yet clear, the Times reported, adding that several private security firms were hired to conduct forensic reviews of infected networks.

Reuters was not able to independently verify the details in the Bloomberg and Times reports. - Reuters