Is Iran planning attacks on Americans; why is the US on alert?

What the report says

US intelligence agencies have warned that Iran is in advanced stages of planning possible attacks on American personnel abroad, according to a memo cited by Al Jazeera and previously reported by Axios and The New York Times. The warning has put US staff in the Middle East on heightened alert and contributed to a reduction in some diplomatic postings in the region. Al Jazeera reported that the memo was sent by Director of National Intelligence Jay Clayton to Secretary of State Marco Rubio, saying Iranian efforts to target US personnel overseas had increased.

The article says US officials view the threat in the Middle East as the most serious it has been since the current US-Israel conflict with Iran began in February. The New York Times, as cited by Al Jazeera, reported that some officials believe Iran has identified potential targets in Europe and that there are indications operatives may already be active inside the United States, though one official said Iran may not be able to carry out all of its plans.

Washington has not publicly discussed the memo, but the State Department has confirmed a drawdown of non-essential staff at the embassy in Saudi Arabia, and other US missions in the region have also reportedly been reduced. Al Jazeera placed the alert in the broader context of rising regional tensions, including attacks by Iran-backed Houthis and reports of possible renewed US-Israeli military action against Iran.

The story also notes that Iran has not directly answered the memo, while Iranian officials have recently warned that Tehran could expand its response if attacked again. Al Jazeera said the US has long accused Iran of plotting against Americans, including alleged attempts tied to President Donald Trump and other officials.