(NewsNation) — The U.S. military conducted a third round of airstrikes against Iran-backed targets in eastern Syria Sunday, and the Biden administration isn’t ruling out the possibility of additional attacks.

It was the third time in less than three weeks that the U.S. targeted areas in Syria tied to Iran. However, the airstrikes were retaliation for ongoing attacks on U.S. troops in Iraq and Syria.

Since the Sunday strikes, U.S. forces were struck by four more militant strikes, all in Syria, a senior defense official told NewsNation. Three of the attacks happened late on Sunday evening and one early Monday morning. It is unclear if any American personnel were injured in these recent attacks.

In the past month, militant groups have carried out a total of 52 drone attacks on American bases in those two countries, injuring dozens of U.S. soldiers.

The strike over the weekend hit facilities used by Iran’s Islamic Revolutionary Guard Corps and Iran-affiliated groups.

NewsNation learned that at least eight pro-Iran fighters were killed in the airstrikes.

On Monday, Defense Secretary Lloyd Austin warned of more strikes unless attacks on U.S. and coalition forces stop.

“These attacks must stop, and if they don’t stop, then we won’t hesitate to do what’s necessary, again, to protect the troops,” Austin told reporters at a news conference in Seoul.

The White House continues to press on Iran and its proxies that they don’t want to see this expand into a wider conflict.

The militant groups began attacking the bases on Oct. 17 after a blast at a Gaza hospital killed hundreds of civilians and further enflamed regional tensions following Hamas’ Oct. 7 attacks inside Israel, where at least 1,200 civilians were killed, and Israel’s blistering military response, which has killed thousands of civilians trapped in Gaza.

In a statement, Defense Secretary Lloyd Austin said the strikes targeted sites near Abukama and Mayadin which were used by Iran’s Revolutionary Guard Corps as well as Iran-backed militias.

President Joe Biden “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,” Austin said.

According to the Pentagon, about 56 U.S. personnel have been injured in the attacks in Syria and Iraq, but all have returned to duty. Their injuries are a combination of traumatic brain injury and other minor wounds.

This is also a topic that could come up in this week’s meeting between President Joe Biden and China’s President Xi Jinping.

Senior administration officials told NewsNation that Biden could make clear in its relationship with Iran that it is essential Iran not seek to escalate or spread violence in the Middle East. 

The Associated Press contributed to this report.