The State Department is reducing staffing at four US embassies in the Middle East after receiving intelligence that Iran has stepped up efforts to target American personnel in the region and elsewhere.

In a memo sent on Friday to Secretary of State Marco Rubio, Director of National Intelligence Jay Clayton said his teams "have received intelligence that Iran has substantially increased efforts to target US personnel."

"The lethal plotting efforts by the Iranians against US citizens have reached advanced stages in both the Middle East and certain other countries," Clayton wrote.

The memo was obtained by The Associated Press and reported earlier by Axios.

There was no immediate reaction from Tehran.

"These materials have been provided to appropriately-cleared senior staff on your team and we are available to brief you at your convenience. We will make every effort to downgrade as much intelligence as possible so you can share it with State Department personnel at your discretion," Clayton added.

Three US officials, speaking on condition of anonymity due to the sensitivity of the matter, confirmed that the memo was sent to Rubio in his capacity as secretary of state and national security adviser.

The memo emerged shortly after the State Department announced it is reducing staff at the US embassies in Jordan, Lebanon, Qatar and the United Arab Emirates.

The three officials said the threats from Iran and Yemen's Houthi militia are related to the staffing changes.

Houthi threat

The embassies involved are all under what is known as "restricted operations" status that has already reduced the size of their personnel footprints. The embassies will remain open.

However, unlike in Saudi Arabia, where nonessential US personnel and their families were ordered Wednesday to leave the country, staff in the other four countries are not compelled to depart.

In announcing the staffing drawdowns this week, the State Department pointed specifically to increased threats from Houthi militias and did not mention threats to US personnel directly from Iran.

US officials have adamantly denied they are tied to any potential new US and Israeli attacks on Iran.