President Joe Biden said that the US would respond “forcefully” to protect its personnel.

Further rocket attacks by Iran-backed militias took place late on Friday, prompting more strikes by coalition warplanes, the Syrian Observatory for Human Rights reported.

Washington carried out the initial strikes after the Pentagon said a US contractor died — and another contractor and five military personnel were wounded — by a drone “of Iranian origin” that struck a US-led coalition base near Hasakah in northeastern Syria on Thursday.

US Defense Secretary Lloyd Austin said that, at President Joe Biden’s direction, he had ordered the “precision airstrikes ... in eastern Syria against facilities used by groups affiliated with Iran’s Islamic Revolutionary Guard Corps.”

On Saturday, the Britain-based Observatory, which has a wide network of sources on the ground, said 19 people were killed in the first wave of US strikes — three Syrian regime soldiers and 16 members of Iran-backed forces, including 11 Syrian nationals. Hours after the strikes, 10 rockets were fired at American and coalition forces at the Green Village base in northeast Syria, the US Central Command said.

There were no injuries or damage to facilities at the base, but one rocket struck a home around five km away, causing minor wounds to two women and two children, CENTCOM added.

Iran-backed militias later on Friday targeted a base in the Conoco gas field, prompting retaliatory strikes from coalition warplanes on targets in Deir Ezzor city, the observatory said.

The war monitor said rocket fire then targeted coalition facilities at the Al-Omar oil field base and in the eastern countryside of Deir Ezzor, “causing material damage.”

A “cautious calm” returned to the Deir Ezzor area in the early hours of Saturday morning, the observatory said.

The Pentagon said two F-15 fighters launched the retaliatory attack — which spokesman Pat Ryder said was to protect US personnel.

The strikes “were intended to send a very clear message that we will take the protection of our personnel seriously and that we will respond quickly and decisively if they are threatened,” he said.

They were “proportionate and deliberate action intended to limit the risk of escalation to minimize casualties,” he said.

Two of the US service members wounded on Thursday were treated on site, while the three other troops and one US contractor were evacuated to Iraq, the Pentagon said.

“We will always take all necessary measures to defend our people and will always respond at a time and place of our choosing,” said CENTCOM chief Gen. Michael Kurilla.

In January, the US military said three one-way attack drones were launched against the Al-Tanf garrison in Syria, with one breaching its air defenses and wounding two allied Syrian fighters. Last August, Biden ordered similar retaliatory strikes in Deir Ezzor province after several drones targeted a coalition outpost, without causing any casualties.

“We know that these groups are sponsored by Iran,” Ryder said.

“So Iran certainly plays a role in terms of ensuring that this type of activity doesn’t happen,” he said.

Meanwhile, Biden said: “The United States does not, does not seek conflict with Iran,” Biden said in Ottawa, Canada, where he is on a state visit. But he said Iran and its proxies should be prepared for the US “to act forcefully to protect our people. That’s exactly what happened last night.”

Biden, speaking during a press conference with Canadian Prime Minister Justin Trudeau, expressed his “deepest condolences” to the family of the American killed and well-wishes for the injured.

US Army Gen. Erik Kurilla, the top US commander for the Middle East, warned that its forces could carry out additional strikes if needed. “We are postured for scalable options in the face of any additional Iranian attacks,” Kurilla said in a statement.