A string of recent cyberattacks against some of the nation's largest banks may have a state sponsor.

Hackers with ties to the government of Iran have waged a series of assaults against as many as nine U.S. financial institutions since September, the Wall Street Journal reported late Friday, citing unnamed American intelligence officials.

The assaults, which reportedly bear electronic fingerprints U.S. authorities have traced to the Persian Gulf state, digitally flood traffic to banks' web servers and slow service for customers who try to retrieve account information.

Capital One (COF), SunTrust Banks (STI) and Regions Financial (RF) all saw their websites slow last week amid the latest wave of denial of service strikes.

A group that calls itself the Izz ad-Din al-Quassam Cyber Fighters claimed responsibility for the onslaught, which continues a campaign the group has waged against U.S. banks since September in retaliation for an American-made, anti-Islamic film.

Though banks have endured similar attacks before, "the scale and speed with which it happened is unprecedented," Defense Secretary Leon Panetta said Thursday in a speech to a business group in New York.

Though Panetta did not charge Iran with being behind the attacks on banks, the secretary said the country has "undertaken a concerted effort to use cyberspace to its advantage." Panetta added that the attacks on banks, together with a recent cyberattack on Saudi Arabia's state-owned oil company and another on a natural gas company in Qatar "have renewed concerns about still more destructive scenarios that could unfold."

The cyberattacks allegedly coming from Iran appear to be the work of a group of roughly 100 digital security specialists, according to the Journal. Friday's report follows news reports in September that the government in Tehran may be targeting banks as part of a broader cyber-offensive in retaliation for cyberattacks by the U.S. against Iran's nuclear program.

For its part, Iran has denied coordinating the attacks. "Iran has not hacked the U.S. banks," Gholam Reza Jalali, head of Iran's Civil Defense Organization, told the FARS News Agency in September.