WASHINGTON (AP) — The U.S. carried out an airstrike on a weapons warehouse in eastern Syria used by Iranian-backed militias, in retaliation for what has been a growing number of attacks on bases housing U.S. troops in the region for the past several weeks, the Pentagon said.

In Wednesday’s strike, two U.S. F-15 fighter jets dropped multiple bombs on a weapons storage facility near Maysulun in Deir el-Zour that was known to be used by Iran’s Revolutionary Guard, U.S. officials said.

“The President has no higher priority than the safety of U.S. personnel, and he directed today’s action to make clear that the United States will defend itself, its personnel, and its interests,” Defense Secretary Lloyd Austin said in a statement.

A military official told reporters in a call that people were seen at the warehouse during the day as the U.S. military watched the site for hours, but the number decreased to about “a couple” overnight when the strike occurred. The official said the strike triggered secondary explosions, indicating the presences of weapons, but the U.S. believes that no civilians were killed and any people at the warehouse were tied to the Revolutionary Guard or militia groups.

The strike, said a senior defense official also on the call, was aimed at “disrupting and degrading the capabilities of groups directly responsible for attacking U.S. forces in the region” by specifically targeting facilities associated with the Revolutionary Guard. Both officials spoke on condition of anonymity to provide an assessment of the strike.

The precision strike, said the defense official, was deliberate and designed not to escalate the conflict in the region. The military official said a deconfliction phone line linking U.S. military personnel to Russian forces in Syria was used to let them know about the attack.

This is the second time in less than two weeks that the U.S. has bombed facilities used by the militant groups, many operating under the umbrella of the Islamic Resistance in Iraq, which U.S. officials say have carried out at least 40 such attacks since Oct. 17.

That was the day a powerful explosion rocked a Gaza hospital, killing hundreds and triggering protests in a number of Muslim nations. The Israeli military has relentlessly attacked Gaza in retaliation for the devastating Hamas rampage in southern Israel on Oct. 7.

Israel denied responsibility for the al-Ahli hospital blast, and the U.S. has said its intelligence assessment found that Tel Aviv was not to blame. But the Israeli military has continued a ferocious assault on Hamas, with ground troops now deep inside Gaza City in a war that has a staggering death toll of more than 10,000 Palestinians, two-thirds of them women and children, according to the Health Ministry of the Hamas-run territory.

The latest U.S. strike was designed to take out supplies, weapons and ammunition in an effort to erode the abilities of the Iranian-backed militants to attack Americans based in Iraq and Syria. And it reflects the Biden administration’s determination to maintain a delicate balance. The U.S. wants to hit Iranian-backed groups suspected of targeting the U.S. as strongly as possible to deter future aggression, possibly fueled by Israel’s war against Hamas, while also working to avoid further inflaming the region and provoking a wider conflict.

Similar U.S. airstrikes on Oct. 27 also targeted facilities in Syria, and officials at the time said the two sites were affiliated with Iran’s Revolutionary Guard. When asked why those locations in Syria were chosen — since many of the attacks have happened in Iraq — officials said the U.S. went after storage sites for munitions that could be linked to the strikes on U.S. personnel.

The U.S. has often avoided bombing sites in Iraq in order to lessen the chances of killing Iraqis or angering Iraq’s leaders.

While officials have said the strikes are meant to deter further attacks, they have not had that effect. Rocket and drone attacks have occurred almost daily, although in nearly all cases they have resulted in little damage and few injuries.

Asked about that, the senior defense official acknowledged that the initial U.S. strike in October did not convince Iran to direct its proxies to stop the attacks. But, the official said, the strikes show America’s willingness to use military force.

According to the Pentagon, a total of 45 personnel have been injured and all of those were in attacks on Oct. 17 and 18. Of those, 32 were at al-Tanf garrison in southeastern Syria, with a mix of minor injuries and traumatic brain injuries, and 13 were at al-Asad air base in western Iraq, with four cases of traumatic brain injury and nine of minor injury. One person was injured at Irbil air base in Iraq.

The Pentagon has faced repeated questions about whether deterrence against Iran and its proxies is working because the attacks have only increased.

At the same time, the department has moved a number of air defense systems and other forces into the region to beef up protection for U.S. forces. And on multiple occasions, the systems have intercepted incoming strikes. According to a U.S. official, the number of ships in the Middle East has more than doubled, the number of Patriot air defense missile systems has about tripled, a few more fighter jet squadrons have been added and hundreds of additional troops have been deployed to the region. The official spoke on condition of anonymity to discuss force numbers not yet made public.