United States President Donald Trump has pledged to pursue “serious retaliation” against ISIL (ISIS) after an ambush in central Syria killed two American soldiers and one civilian interpreter.

An investigation is under way to determine whether the attacker was linked to ISIL, but Trump on Saturday blamed the armed group that had seized territories across Syria and Iraq in 2014.

The attack on US forces was the first to inflict casualties since the fall of Syrian President Bashar al-Assad a year ago.

Three US military members were injured in the attack, as well as at least two Syrian soldiers, according to government and media reports.

Trump said in a social media post he had received confirmation that the injured US soldiers were “doing well”.

He, however, warned that there would be serious consequences for what he described as an ISIL attack.

“This was an ISIS attack against the U.S., and Syria, in a very dangerous part of Syria, that is not fully controlled by them,” Trump wrote. “The President of Syria, Ahmed al-Sharaa, is extremely angry and disturbed by this attack. There will be very serious retaliation.”

His remarks echoed those of Defense Secretary Pete Hegseth, who likewise promised to take severe action against anyone who attacked US service members.

“Let it be known, if you target Americans — anywhere in the world — you will spend the rest of your brief, anxious life knowing the United States will hunt you, find you, and ruthlessly kill you,” Hegseth wrote on social media.

Counterterrorism operations

Saturday’s attack was first announced by the US Central Command, also known as CENTCOM.

It characterised the attack as an “ambush” carried out by a lone ISIL gunman, who was subsequently “engaged and killed”. Hegseth later said the perpetrator “was killed by partner forces”.

The attack took place near Palmyra in Syria’s central Homs region, according to Pentagon spokesperson Sean Parnell.

“The attack occurred as the soldiers were conducting a key leader engagement,” he wrote in a statement. “Their mission was in support of on-going counter-ISIS/counter-terrorism operations in the region.”

Tom Barrack, the US ambassador to Turkiye, meanwhile, described the incident on X as a “cowardly terrorist ambush targeting a joint U.S.–Syrian government patrol”. He noted there were “Syrian troops wounded in the attack” and wished them a “speedy recovery”.

But the details about the attack and the individuals involved remain unclear.

CENTCOM indicated the US government would withhold identifying information about the late US soldiers and their units “until 24 hours after their next of kin have been notified”.

The incident remains under “active investigation”, according to the US Defense Department.

Myles Caggins, a retired US Army colonel and former spokesperson for the Coalition to Defeat ISIS, told Al Jazeera that there had been “conflicting messages” around the attack.

In his most recent statement, the director of the US National Counterterrorism Center, Joe Kent, had indicated that the incident “was an insider attack, what we often would call a green-on-blue attack”, while Barrack, the US ambassador to Turkiye, had “backed away from language attributing this to ISIS”, Caggins said.

He said, in response, the US had conducted “a show of force” by dropping flares around the city of Palmyra, but would now likely move on from the incident.

“In reality, the attack is over, the attacker has been killed, and we must move to the next steps,” he said.

Who was the suspect?

The identity of the suspect has also not been released to the public.

But three local officials told the Reuters news agency that the assailant was a member of Syrian forces.

A spokesperson for the Syrian Ministry of Interior also told Al-Ikhbariah TV that the attacker did not have a leadership role in the country’s security forces. He did not say whether the man was a junior member.

“On December 10, an evaluation was issued indicating that this attacker might hold extremist ideas, and a decision regarding him was due to be issued tomorrow, on Sunday,” the spokesperson, Noureddine el-Baba, said.

The official Syrian Arab News Agency (SANA) reported earlier that Syrian forces and US troops came under fire during a joint patrol.

The AFP news agency, meanwhile, quoted an anonymous Syrian military official as saying shots were fired “during a meeting between Syrian and American officers” at a Syrian base in Palmyra.

A witness in the city, who requested anonymity, told AFP that he heard the shots from inside the base.

Traffic on the Deir Az Zor-Damascus highway was temporarily halted as military aircraft conducted overflights in the area, AFP reported.

A security source told SANA that US helicopters evacuated the wounded to the al-Tanf base near the Iraqi border.

A long-term US presence

In the aftermath of the attack, US officials pledged to double down on their efforts to combat ISIL.

“We will not waver in this mission until ISIS is utterly destroyed, and any attack on Americans will be met with swift and unrelenting justice,” Ambassador Barrack posted on social media.

“Alongside the Syrian Government, we will relentlessly pursue every individual, facilitator, financier, and enabler involved in this heinous act. They will be identified and held accountable swiftly and decisively.”

The US has troops stationed in northeastern Syria as part of a decade-long effort to help a Kurdish-led force there combat ISIL.

ISIL captured Palmyra in 2015, at the height of its military ascendancy in Syria, before losing the city 10 months later. During that time, it destroyed several ancient sites and artefacts while using others to stage mass killings.

ISIL was vanquished in Syria in 2018 but still carries out sporadic attacks without controlling any territory inside Syria.

As of December 2024, there were approximately 2,000 US soldiers stationed in Syria to continue the fight against ISIL.

In late November, CENTCOM announced the destruction of “more than 15 sites containing ISIS weapons caches”, as the US continues its campaign against the armed group.

Caggins, the retired colonel, told Al Jazeera that Trump and al-Sharaa “have a new but strong relationship built on admiration for each other” and the US had been successfully partnering with the new Syrian transitional government on anti-ISIL operations in the northwest and in the desert regions.

Earlier this month, Syria marked one year since the ousting of longtime leader al-Assad, but the war-ravaged nation continues to face stiff security and economic challenges as it seeks to rebuild and recover after 14 years of ruinous civil war.