The attack, Bloomberg said, led to the loss of sensitive data. It did not elaborate. The New York Times, quoted sources as saying JP Morgan and at least four other firms were hit this month by co-ordinated attacks which siphoned off huge amounts of data, including customer account information. Bloomberg cited security experts saying that the attack appeared "far beyond the capability of ordinary criminal hackers."
The FBI said it was investigating the reports without confirming details.
"We are working with the United States secret service to determine the scope of recently reported cyber-attacks against several American financial institutions," a spokesman said.
The US has introduced a number high-level sanctions against Russian leaders and industries over the conflict in Ukraine between the government and Russian-backed separatists.