WASHINGTON (AP) — The U.S. military launched airstrikes early Friday on two locations in eastern Syria linked to Iran’s Revolutionary Guard Corps, the Pentagon said, in retaliation for a slew of drone and missile attacks against U.S. bases and personnel in the region that began early last week.

The U.S. strikes reflect 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 inflaming the region and provoking a wider conflict.

According to the Pentagon, there have been at least 12 attacks on U.S. bases and personnel in Iraq and four in Syria since Oct. 17. Air Force Brig. Gen. Pat Ryder said 21 U.S. personnel were injured in two of those assaults that used drones to target al-Asad Airbase in Iraq and al-Tanf Garrison in Syria.

In a statement, Defense Secretary Lloyd Austin said the “precision self-defense strikes are a response to a series of ongoing and mostly unsuccessful attacks against U.S. personnel in Iraq and Syria by Iranian-backed militia groups that began on October 17.”

He said President Joe Biden directed the narrowly tailored strikes “to make clear that the United States will not tolerate such attacks and will defend itself, its personnel, and its interests.” And he added that the operation was separate and distinct from Israel’s war against Hamasa.

Austin said the U.S. does not seek a broader conflict, but if Iranian proxy groups continue, the U.S. won’t hesitate to take additional action to protect its forces.

According to the Pentagon, all the U.S. personnel hurt in the militant attacks received minor injuries and all returned to duty. In addition, a contractor suffered a cardiac arrest and died while seeking shelter from a possible drone attack.

The retaliatory strikes came as no surprise. Officials at the Pentagon and the White House have made it clear for the past week that the U.S. would respond, with Ryder saying again Thursday that it would be “at the time and place of our choosing.”

“I think we’ve been crystal clear that we maintain the inherent right of defending our troops and we will take all necessary measures to protect our forces and our interests overseas,” he told reporters during a Pentagon briefing earlier in the day.

The latest spate of strikes by the Iranian-linked groups came in the wake of a deadly explosion at a Gaza hospital, 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 nearly three weeks ago, but Israel has 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.

The U.S., including the Pentagon, has repeatedly said any strike response by America would be directly tied to the attacks on the troops, and not connected to the war between Israel and Hamas. Such retaliation and strikes against Iranian targets in Syria after similar attacks on U.S. bases are routine.

In March, for example, the U.S. struck sites in Syria used by groups affiliated with Iran’s Revolutionary Guard after an Iranian-linked attack killed a U.S. contractor and wounded seven other Americans in northeast Syria. American F-15 fighter jets flying out of al-Udeid Air Base in Qatar struck several locations around Deir el-Zour.

U.S. officials have routinely stressed that the American response is designed to be proportional, and is aimed at deterring strikes against U.S. personnel who are focused on the fight against the Islamic State group.

U.S. officials have not publicly tied the recent string of attacks in Syria and Iraq to the violence in Gaza, but Iranian officials have openly criticized the U.S. for providing weapons to Israel that have been used to strike Gaza, resulting in civilian death.