U.S. President Joe Biden has said the United States does not seek conflict with Iran but will respond to protect its personnel in Syria and elsewhere.
The United States is prepared "to act forcefully to protect our people. That's exactly what happened last night," Biden said after he ordered a retaliatory air strike on sites in Syria used by groups affiliated with Iran's Islamic Revolutionary Guards Corps (IRGC).
Biden, who spoke to reporters during a visit to Ottawa, Canada, ordered the air strike after a U.S. contractor was killed and six other Americans were injured in an attack on March 23 blamed on groups affiliated with Iran in northeast Syria.
The deadly attack by a kamikaze drone struck a maintenance facility on a base of the U.S.-led coalition near Hasakeh in northeastern Syria, the Pentagon said.
The United States has maintained about 900 troops in posts across northeastern Syria to keep pressure on groups affiliated with the Islamic State group and to support the Kurdish-led Syrian Democratic Forces in their fight against the Syrian government.
The Pentagon said two F-15 fighters launched the retaliatory attack early on March 24. According to the Syrian Observatory for Human Rights, the attack killed 11 pro-Iranian fighters -- six at a weapons depot in Deir el-Zour city and five others at military posts near two towns.
Two Syrian opposition activist groups later on March 24 reported a new wave of air strikes in eastern Syria against positions of Iran-backed militias.
The new wave of air strikes came after rockets were fired at a Conoco gas plant that has a base housing U.S. troops. It was not immediately clear if U.S. warplanes carried out the attack.
U.S. Defense Secretary Lloyd Austin said in the Pentagon statement that the U.S. intelligence community had determined the drone that killed the U.S. contractor was of Iranian origin but offered no evidence to support the claim.
The statement said its retaliatory "precision" strikes were intended to protect and defend U.S. personnel and were "proportionate and deliberate" and intended to limit the risk of escalation and minimize casualties.
"As President Biden has made clear, we will take all necessary measures to defend our people and will always respond at a time and place of our choosing," Austin said. "No group will strike our troops with impunity."