(NewsNation) — At least 21 U.S. service members have been injured as a result of rocket and drone attacks on military bases in Syria and Iraq since last week, according to the Pentagon.

Now, roughly 900 U.S. troops have deployed or are deploying to the Middle East, the Pentagon said Thursday. Those forces will support “regional deterrence efforts” and are not going to Israel.

Since Oct. 17, there have been 16 attacks against U.S. troops and coalition forces in the Middle East — 12 in Iraq and four in Syria. All of those have come from groups affiliated with Iran, per the Pentagon.

On Wednesday, President Joe Biden issued a direct message to Iran’s leader.

“My warning to the Ayatollah was that if they continue to move against those troops, we will respond, and he should be prepared,” Biden said. “It has nothing to do with Israel.”

Around the time of that statement, the Pentagon learned of another attack against U.S. forces in Iraq, although nobody was injured.

So far, the assaults have resulted in “minor injuries,” according to the Pentagon. However, 19 service members were diagnosed with traumatic brain injuries. All have since returned to duty.

The attacks come amid simmering tensions in the region following the outbreak of war between Israel and Hamas.