A sixth U.S. service member was wounded after a contractor was killed Thursday.
A U.S. official told ABC News that there were two new attacks late Friday on two U.S. facilities in Deir ez-Zor Province in eastern Syria after another earlier in the day and a drone attack on Thursday that prompted retaliatory U.S. airstrikes that targeted Iranian-backed militias believed responsible.
Both attacks late Friday happened about the same time, the official said. One involved three drones targeting one facility and the other involved five rockets fired at a separate facility, according to the official, who said one American service member was wounded and was in stable condition.
NOTE: The video in the media player is from a previous report.
The official said that two of the three drones that targeted one U.S. facility were shot down, but one drone made it through. There were no injuries in that attack.
The official said that five rockets were fired at another U.S. facility where the American service member was wounded. That individual is in stable condition, the official said, and that a damage assessment of the facility was still underway.
Earlier Friday, a Pentagon spokesman said the first attack on a U.S. base did not cause any damage and there were no injuries.
"On the morning of March 24th, at approximately 8:05 am local time, 10 rockets targeted coalition forces at the Green Village in northeast Syria," said Lt. Col. Phil Ventura, a Pentagon spokesman.
"The attack resulted in no injuries to US or coalition personnel and no damage to equipment or facilities," he added.
The new attacks, of which there have been about 80 since the start of 2021, come a day after the U.S. military conducted retaliatory airstrikes in eastern Syria on Thursday against Iranian-backed groups after a one-way explosive drone attack targeting a U.S. base in the region killed a U.S. contractor and injured six others, including five U.S. service members, the Pentagon said.
"Earlier today, a U.S. contractor was killed and five U.S. service members and one additional U.S. contractor were wounded after a one-way unmanned aerial vehicle struck a maintenance facility on a Coalition base near Hasakah in northeast Syria at approximately 1:38 p.m. local time," the Pentagon said in a statement.
Two of the wounded service members were treated on site, while the other four Americans were medically evacuated to coalition medical facilities in Iraq, officials said. A U.S. official confirmed to ABC News that both contractors were American.
U.S. intelligence assessed that the one-way attack drone that struck the base on Thursday was Iranian in origin, according to the statement. Iran has used such drones in the past in attacks on Saudi Arabia and in Yemen, but this drone technology has become more noticeable after it provided hundreds of Shahed drones to Russia that have been used in attacks against Ukrainian civilians and infrastructure targets.
Earlier on Thursday, Gen. Michael "Erik" Kurilla, who as the commander of U.S. Central Command is the top U.S. military commander in the Middle East, told Congress that there have been 78 such attacks since the beginning of 2021.
"At the direction of President [Joe] Biden, I authorized U.S. Central Command forces to conduct precision airstrikes tonight in eastern Syria against facilities used by groups affiliated with Iran's Islamic Revolutionary Guards Corps (IRGC)," Defense Secretary Lloyd J. Austin III said in the statement, issued late Thursday.
"The airstrikes were conducted in response today's attack, as well as a series of recent attacks against Coalition forces in Syria by groups affiliated with the IRGC," he added.
A U.S. official told ABC News that the airstrikes were carried out by U.S. Air Force F-15 fighter aircraft as part of a response approved by President Joe Biden earlier on Thursday.
Biden was enroute to Ottawa, Canada, when he approved the airstrikes presented by the Pentagon and the U.S. intelligence community as response options to the drone attack, White House spokesman John Kirby said during an appearance on CNN.
"He made the decision very, very shortly in that discussion to authorize the strikes against these particular targets," Kirby said. "We're going to work to protect our people and our facilities as best we can. It's a dangerous environment."
"We are not seeking a conflict with Iran," said Kirby. "We've been very clear with the Iranians and with our partners about how serious the mission that we're doing in Syria is and how we're going to protect that mission."
"Iran should not be involved in supporting these attacks on our facilities or on our people, we've made that very very clear," said Kirby.
At a news conference with Canada's Prime Minister Justin Trudeau Friday afternoon, before the reports of even more attacks, Biden said, "make no mistake, the United States does not -- does not, emphasize -- seek conflict with Iran but be prepared for us to act forcefully protect our people. That's exactly what happened last night."
The U.S. has about 900 troops in eastern Syria providing assistance to Syrian Kurdish forces in preventing a resurgence of the Islamic State.
In recent months, some of the bases have been the target of drone attacks that had, in most instances, not led to injuries or physical damage. Iranian-backed groups in Syria are believed to have been responsible for these attacks.
"These precision strikes are intended to protect and defend U.S. personnel. The United States took proportionate and deliberate action intended to limit the risk of escalation and minimize casualties," the Pentagon statement read.
"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."
"Our thoughts are with the family and colleagues of the contractor who was killed and with those who were wounded in the attack earlier today," the defense secretary added.
In a statement, U.S. Central Command leader Gen. Michael "Erik" Kurilla said, in part, that the U.S. "will always take all necessary measures to defend our people and will always respond at a time and place of our choosing. We are postured for scalable options in the face of any additional Iranian attacks."
"Our troops remain in Syria to ensure the enduring defeat of ISIS, which benefits the security and stability of not only Syria, but the entire region," he added.
During Thursday's House Armed Services Committee hearing focused on the Middle East and Africa, Kurilla was asked by Nebraska Rep. Don Bacon about the frequency of Iranian proxy attacks on U.S. forces.
There have been 78 such attacks since the beginning of 2021, according to Kurilla.
"It is periodic. We see periods where they will do more," he said
"So what Iran does to hide its hand is they use Iranian proxies -- that's under UAVs or rockets -- to be able to attack our forces in Iraq or Syria," Kurilla added.
ABC News analyst Mick Mulroy, former deputy assistant secretary of defense for the Middle East and retired CIA officer, said the U.S. "must strike back at the Iranian forces in Syria responsible for these attacks to such an extent that they know the consequences of killing and injuring Americans will not be worth the costs."