U.S. President Joe Biden ordered strikes on two facilities in Syria following attacks on U.S. troops in the past week, the Pentagon said, warning the U.S. will take additional measures if attacks by Iran’s proxies continue.

U.S. forces have been hit more than a dozen times in Iraq and Syria in the past week by what Washington suspects are Iran-backed groups. Hamas, Islamic Jihad and Lebanon’s Hezbollah are all backed by Tehran.

Iranian Foreign Minister Hossein Amirabdollahian said at the United Nations on Thursday that if Israel’s offensive against Hamas did not stop, the United States will “not be spared from this fire”.

The U.S. military carried out strikes on Thursday against two facilities in eastern Syria used by Iran’s Islamic Revolutionary Guard Corps and groups it backs, the Pentagon said.

“These precision self-defence 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,” U.S. Defense Secretary Lloyd Austin said in a statement.

“These Iranian-backed attacks against U.S. forces are unacceptable and must stop,” Austin said.

Biden has sent a rare message to Iranian Supreme Leader Ayatollah Ali Khamenei warning Tehran against targeting U.S. personnel in the Middle East, the White House said earlier on Thursday.

Israel said on Friday military raids into Gaza were preparing “the next stage of the operation”, amid fears that a ground invasion of the Palestinian enclave could spark a wider Middle East conflict.