Sen. Joe Lieberman (Conn.) said Friday that reported cyber attacks against major American financial institutions were likely sponsored by Iran and were in retaliation for sanctions imposed on the country by the United States and its allies.

In a taped appearance on C-SPAN's "Newsmakers," Lieberman said he believed reported attacks against the banks “were not done just by random hackers” and that there was “some basis for believing this was an Iranian-sponsored attack.”

“I believe it was in response to the increasingly strong economic sanctions that the United States and our European allies have put on Iranian financial institutions,” said Lieberman, who is chairman of the Homeland Security and Governmental Affairs Committee. "It is, if you will, a counter attack by Iran against American financial institutions."

He called the attacks a "powerful example of our vulnerability."

Iranian hackers have repeatedly disrupted websites belonging to Bank of America, JPMorgan Chase and Citigroup, Reuters reported on Friday, citing sources familiar with the situation. The attacks, which began last year and flooded their websites with traffic, appeared to be in retaliation to the banks' enforcement of economic sanctions against the country, according to Reuters.

Spokespeople for the Department of Homeland Security, the Secret Service and the FBI declined to comment on the reports.

Earlier this week, the Financial Services Information Sharing and Analysis Center raised its cyber threat level to "high" from "elevated." The center warned banks of "recent credible intelligence" about potential cyber attacks against financial institutions "that could make companies' websites unusable for customers."

On Tuesday, Bank of America customers reported the bank’s website was periodically down. A bank spokesman told The Huffington Post the site was still available, “although some customers may experience occasional slowness.”

On the same day, a hacker group calling using the name the “QassamCyberFighters” posted a statement on the file-sharing site Pastebin claiming responsibility for cyber attacks against Bank of America and the New York Stock Exchange.

But the hackers’ claim was "a cover” for attacks that were carried out by the government of Iran, a source told NBC News, which reported the cyber attacks against the banks were "significant and ongoing."

Experts have repeatedly warned about Iran's ability to launch cyber attacks. In April, Ilan Berman, vice president of the American Foreign Policy Council, told a House panel that the Iranian regime has invested heavily in building up its cyber capabilities and has expressed an increasing desire to use it.

On Thursday, Frank J. Cilluffo, director of the Homeland Security Policy Institute, told the House Committee on Homeland Security that “the government of Iran and its terrorist proxies are serious concerns in the cyber context.”

“What Iran may lack in capability, it makes up for in intent,” he said at the hearing, where his appearance had already been scheduled before the reports surfaced.

Iran has been on the receiving end of cyber attacks in the past. Most notably, the United States, along with Israel, launched a series of cyber attacks that damaged Iran's nuclear program.

The computer worm used in the attack, known as Stuxnet, was discovered in 2010 and is considered the most powerful cyberweapon ever created.

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