The FBI is investigating the public disclosure of a pair of highly classified intelligence documents describing Israel's preparations for a retaliatory strike on Iran, the bureau said on Tuesday.

The suspects planned to assassinate two people, a senior Israeli scientist and the mayor of a large Israeli city, authorities said.

President Joe Biden is "deeply concerned" about a leak of classified documents that contain the US's assessment of Israeli plans to attack Iran, White House National Security Council spokesman John Kirby said. Officials have not determined whether the documents were released due to a hack or a leak, Mr Kirby said.

Foreign powers are likely to aim to promote protests disputing the presidential-election results, officials said.

Russia and Iran may seek to foment violent protests inside the US in the days and weeks after the Nov. 5 election as voting results are being tabulated and certified, US intelligence agencies warned on Tuesday.

Russia, Iran and China are intent on fanning divisive narratives to divide Americans ahead of the Nov. 5 U.S. elections, an American intelligence official said on Tuesday, although they are unlikely to be able to manipulate the contests at a scale that would affect the outcome of the presidential race.