Handala, an Iran-linked hacker group, threatened on Thursday to breach the FBI's computer systems.
In an update posted to the group's Telegram channel, Handala previewed what it said would be one of the biggest security breaches of the decade.
"FBI breach coming soon," the Telegram post read. "Soon you will realise that the FBI's security was nothing more than a joke."
The FBI declined to comment.
The threat came a day after Handala claimed that US aerospace and defence company Lockheed Martin had been compromised.
"The manufacturer of the F-35, F-22, Thaad missile defence system and advanced electronic warfare systems could not even protect its own identity," the group said on Wednesday.
In a statement to The National, a Lockheed Martin representative did not confirm that its systems had been compromised.
"Lockheed Martin continues to carry out its mission-critical work in support of American and allied warfighters around the world," the statement read.
"We are aware of the reports and have policies and procedures in place to mitigate cyber threats to our business." It said that Lockheed Martin remained confident in its "multi-layered information systems".
Last week, the US Justice Department and FBI announced the seizure of several websites associated with Handala.
The filings related to the seizures also confirm that Handala was responsible for a recent cyber attack against Michigan-based medical technology company Stryker, which has more than 50,000 employees around the world.
The US alleges that Handala might also be responsible for cyber attacks on hospitals and medical services in Maryland.
“We took down four of their operation's pillars and we're not done,” said FBI director Kash Patel after the Justice Department announced the seizure of several Handala internet properties, adding that the US would “hunt down every actor behind these cowardly death threats and cyber attacks”.
Yet the seizures by the US government seem to have had little impact on the group.
“The seizure of our domains, propaganda bombardment, threats of assassination, and even the looming shadow of aerial bombardment are nothing more than the latest desperate attempts by the United States and its allies to silence the voice of Handala,” a recent post by the group on Telegram read.
Ever since US and Israeli air strikes on Iran started on February 28, cyber-security analysts have warned of an increase in potential cyber attacks from Tehran and groups seeking to take advantage of the situation.
Several months before the US and Israeli strikes, Microsoft's security division warned that Iran shows no sign of slowing its cyber attacks.
Meanwhile, according to internet monitor NetBlocks, Iran has entered the 27th day of its self-imposed internet blackout that is affecting 99 per cent of the country.
"Rights monitors, independent media and the public are sidelined as access is granted only to those on a state-approved white list," NetBlocks said.
