The online sites of the nation's biggest banks seem to be functioning without interruption following a hacktivist threat to launch a series of cyberattacks on financial institutions and government agencies.

JPMorgan Chase (JPM), Bank of America (BAC), Citigroup (NYSE:C), Wells Fargo (WFC) and dozens of others ran mostly without digital delays on Tuesday, according to Sitedown.co, which tracks online outages.

The hacker collective Anonymous and other groups vowed to wage a series of so-called denial of service attacks, according to a message posted April 24 on Pastebin, a website used by programmers.

Earlier this week, the Al Qassam Cyber Fighters, a group that has claimed responsibility for a series of denial of service attacks since September that have rendered online and mobile banking inoperable at some of the nation's biggest financial institutions, said it planned to suspend its campaign through Thursday to avoid sowing confusion between its operation and the attacks threatened by Anonymous.

On Tuesday afternoon, however, networks used by the attackers - who have dubbed the effort OpUSA - showed low rates of activity, according to digital software security firm Radware, which is monitoring the threats.

The warnings follow a similar campaign against commercial and government targets in Israel by Anonymous, which has claimed responsibility for attacks on companies in that country that experts say was relatively unsophisticated in its approach.

The threat posed by the assaults depended on whether hacktivists could commandeer cloud computing facilities, which can ratchet up the velocity of barrages on websites that occur in a denial of service attack significantly, according to experts. "If we don't see that, it will be like Operation Israel," Carl Herberger, vice president of security solutions at Radware, told American Banker.

Banks had been warned by the federal government to expect "nuisance-level attacks against publicly accessible webpages and possibly data exploitation," according to a bulletin issued by the Department of Homeland Security obtained by information security blog Krebs on Security.

"Independent of the success of the attacks, the criminal hackers likely will leverage press coverage and social media to propagate an anti-U.S. message," said DHS in the missive.

The campaign comes in retaliation for what supporters said are American war crimes in Afghanistan, Iraq and Pakistan.