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The FBI announced Tuesday it was investigating the alleged leak of classified US intelligence documents about Israel's plans for a retaliatory strike on Iran.
Iran has been bracing for a response since it unleashed a wave of close to 200 ballistic missiles on Israel on October 1 in retaliation for the killings of Tehran-backed senior figures in Hamas and Hezbollah.
The classified documents, circulated on the Telegram app last week by an account called Middle East Spectator, describe Israeli preparations for a possible strike -- but do not identify any actual targets.
"The FBI is investigating the alleged leak of classified documents and working closely with our partners in the Department of Defense and Intelligence Community," the FBI said in a statement.
White House national security spokesman John Kirby told reporters on Monday that US authorities were unaware if the documents had been leaked or hacked.
"We're not exactly sure how these documents found their way into the public domain," Kirby said, adding that such a leak would be "unacceptable."
President Joe Biden had indicated last week that his administration was privy to Israel's plans, answering "yes and yes" to a reporter who asked if he had "a good understanding" of how and when Israel would respond.
Republican presidential candidate Donald Trump seized upon the apparent leak Tuesday, painting it as an example of government incompetence.
"They leaked all the information about the way that Israel is going to fight, and how they're going to fight, and where they're going to go," the former US president said, exaggerating the actual content of the classified material.
"Can you imagine somebody doing that? That's the enemy, I guess, that maybe is the enemy from within," Trump said -- using a formula for describing political opponents that has become a persistent refrain at his campaign events.