Russian hackers stole data from JPMorgan Chase and at least one other bank in a mid-August attack against the U.S. financial system, according to a Bloomberg news report.

The FBI is investigating whether the attacks were possible retaliation for U.S.-sponsored economic sanctions against Russia, Bloomberg reports, citing two people familiar with the probe.

When contacted by Information Security Media Group, the FBI declined to comment on the news report.

JPMorgan Chase is the largest financial institution in the U.S., with $2.48 trillion in total assets as of March 31, according to the FFIEC.

The attack allegedly resulted in the loss of "gigabytes" of sensitive data, Bloomberg reports. Authorities are also investigating whether recent intrusions of major European banks using a similar vulnerability are also linked to the U.S. attack, according to the report.

One of the alleged bank compromises involved hackers exploiting a zero-day vulnerability, the news report states. The hackers then worked their way through layers of security to steal sensitive information, "a feat security experts said appeared far beyond the capability of ordinary criminal hackers," according to the report.

Patricia Wexler, a JPMorgan spokesperson, told Bloomberg: "Companies of our size unfortunately experience cyber-attacks nearly every day. We have multiple layers of defense to counteract any threats and constantly monitor fraud levels."