U.S. military aircraft have carried out strikes in eastern Syria against facilities associated with Iranian-backed militant groups believed to be responsible for more than a dozen rocket and drone attacks on American troops in Iraq and Syria that injured 21 service members, the military said Thursday night.

“Today, at President Biden’s direction, U.S. military forces conducted self-defense strikes on two facilities in eastern Syria used by Iran’s Islamic Revolutionary Guard Corps (IRGC) and affiliated groups,” said Defense Secretary Lloyd Austin in a statement.

“These 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.

“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 not tolerate such attacks and will defend itself, its personnel, and its interests,” he added.

The retaliatory operations were carried out at a time of heightened tensions in the Middle East amid the ongoing Israel-Hamas war, in the wake of Hamas’ terror attack on Israel on Oct. 7, and U.S. concerns about preventing that conflict from enveloping the rest of the region.

“The United States does not seek conflict and has no intention nor desire to engage in further hostilities, but these Iranian-backed attacks against U.S. forces are unacceptable and must stop,” Austin continued. “Iran wants to hide its hand and deny its role in these attacks against our forces. We will not let them. If attacks by Iran’s proxies against U.S. forces continue, we will not hesitate to take further necessary measures to protect our people.”

America has deployed two aircraft carriers as well as additional fighter squadrons and air defense systems to the Middle East to deter Iran or Hezbollah, the Iran-sponsored militant group that operates in southern Lebanon, from getting involved by launching a wider assault on Israel.

Senior U.S. officials have publicly blamed Iran for the more than 16 drone and rocket attacks on military bases in Iraq and Syria over the past week, which the U.S. believes have been carried out by Iranian-backed militant groups.

Twenty-one service members have been injured, according to the Pentagon’s latest information. Officials said all of those troops returned to duty after experiencing minor injuries or traumatic brain injuries, but an American civilian contractor died from a cardiac arrest that occurred during one of the attacks.

On Wednesday, President Joe Biden stressed that the U.S. reserves the right to retaliate.