Iran was behind last week's attacks on the Web sites of Bank of America and JP Morgan Chase, targeting the pair in retaliation for Western economic sanctions, according to US media reports.
The BofA and Chase sites both saw their online presences disrupted by Distributed Denial of Service attacks last week in what was initially reported to be a response to the release of a US movie mocking the prophet Mohammed.
However, citing sources, Reuters says that the US believes that the actions were just part of a broader campaign against American targets that has seen both banks, as well as Citi, under fire since late last year.
Reuters' sources say that the attacks originated in Iran but it is not clear whether they were carried out by the government or groups working on its behalf.
US Senator Joseph Lieberman has also pointed the finger, telling C-Span he believes the DDoS efforts were a response to "the increasingly strong economic sanctions that the United States and our European allies have put on Iranian financial institutions".
The claims have been dismissed by Iran though, with Gholam Reza Jalali, head of its civil defence organisation, telling the Fars News Agency: "Iran has not hacked the US banks."
The US is not adverse to using cyber-warfare itself - it is widely accepted to have worked with Israel on Stuxnet, the virus that famously hit Iran's uranium enrichment programme in 2010.