About 900 more US troops have arrived in the Middle East or are heading there to bolster air defenses for US personnel amid a surge in attacks by Iran-affiliated groups, the Pentagon said on Thursday.

As tensions soar over the Israel-Hamas war, US and coalition troops have been attacked at least 12 times in Iraq and four times in Syria in the last week, Pentagon spokesperson Brigadier General Patrick Ryder told reporters.

A total of 21 US forces have suffered minor injuries, the vast majority of them traumatic brain injuries.

The United States has sent warships and fighter aircraft to the region since the conflict erupted on Oct. 7, including two aircraft carriers, to try to deter Iran and Iran-backed groups. The number of troops added to the region is in the thousands.

Ryder said US forces were again targeted earlier on Thursday in Iraq but the attack failed.

“I’m not going to have more specific information to provide to you from here in terms of specific groups that have claimed responsibility (for attacking US personnel), other than to say we know that these groups are affiliated with Iran,” Ryder said.

Reuters reported this week the US military was taking new measures to protect its Middle East forces during the ramp-up in attacks by suspected Iran-backed groups, and was leaving open the possibility of evacuating military families if needed.

The measures include increasing US military patrols, restricting access to base facilities and boosting intelligence collection, including through drone and other surveillance operations, officials say.

The US is also beefing up monitoring from guard towers on its military facilities, increasing security at base access points and increasing operations to counter potential incoming drones, rockets and missiles, the officials say.

The latest US troop deployments are tied to US plans to deploy a Terminal High Altitude Area Defense (THAAD) system and Patriot missile batteries.

Iranian Foreign Minister Hossein Amirabdollahian told the United Nations on Thursday that if Israel’s retaliation against Palestinian Hamas militants in the Gaza Strip does not end, then the United States will “not be spared from this fire.”

Last week off the coast of Yemen, a US warship shot down more than a dozen drones and four cruise missiles fired by Iranian-backed Houthis.

The heightened tensions have put US personnel on constant alert. 

During a false alarm at Al-Asad air base in Iraq on Thursday, a civilian contractor died from cardiac arrest.