The US Department of Defense reported at least 3,500 troops will be deployed in the Middle East.

It is a defensive measure in the wake of Iran's harsh retaliation after the US killed the commander-in-chief of the Iranian Revolutionary Guard's elite commander Kuds Soleimani in a drone air strike.

In the United States, concerns about Iran's retaliation are growing.

The Washington Post reported that the Pentagon will deploy an additional 3,500 troops from the 82nd Airborne Division in the Middle East to strengthen the region's defenses.

An official, who requested anonymity, said the additional deployment would join the 750 troops who arrived in Kuwait yesterday.

US Defense Secretary Mark Esper said Monday he has dispatched 750 troops from the 82nd Airborne Division Rapid Response Force in response to an attack on the US embassy in Baghdad, Iraq, and is preparing a separate deployment.

AFP also quoted US officials as saying that troops will be deployed in Kuwait as appropriate and preventive measures in response to increased threats to Americans and US facilities.

Reuters also said it had deployed more than 3,000 troops, saying the United States has deployed an additional 14,000 troops in the Middle East since May last year.

The US deployment of the Middle East is noted as a defense against Iran's proclamation of harsh retaliation after the US killing commander of the Iranian Revolutionary Guard's elite commander Kuds Soleimani.

There are concerns in the United States that Americans and US facilities in the Middle East could be targets of retaliation in Iran.

The United States has already ordered all US citizens in Iraq to leave immediately.

The Department of Homeland Security made a statement and said there are no threats to the mainland.

The Department of Homeland Security said, "There are no specific and reliable threats to the US mainland, and we are ready to fight any threats to the mainland."