Syrian forces and a United States-led coalition launched an operation against Isis sleeper cells today, a Syrian Interior Ministry official said, a day after a deadly attack on US troops in the country.

Two US troops and a civilian interpreter were killed in what the Syrian Government described as a “terrorist attack”, while Washington said it had been carried out by an Isis militant who was subsequently killed.

The ministry official, who requested anonymity, told AFP that a “security campaign” across the Syrian desert was tracking “Daesh sleeper cells, in co-operation with the US-led international coalition”, using the Arabic acronym for Isis.

The official said three individuals have so far been arrested over their suspected involvement in the Sunday attack, which took place in central Syria’s Palmyra region.

Syrian President Ahmed al-Sharaa sent a message of condolences to his US counterpart Donald Trump, expressing his country’s “solidarity with the victims’ families”.

Syrian authorities had earlier said that the perpetrator was a member of the security forces who was due to be fired today for his “extremist Islamist ideas”, Interior Ministry spokesman Noureddine al-Baba told state television.

A Syrian security official told AFP today that “11 members of the general security forces were arrested and brought in for questioning after the attack”.

The security official, who spoke on condition of anonymity, said the gunman had belonged to the security forces “for more than 10 months and was posted to several cities before being transferred to Palmyra”.

Palmyra, home to Unesco-listed ancient ruins, was controlled by Isis at the height of its territorial expansion in Syria.

‘Serious retaliation’

The incident is the first of its kind to be reported since Islamist-led forces overthrew longtime Syrian ruler Bashar al-Assad in December last year and rekindled the country’s ties with the US.

Trump vowed “very serious retaliation” following yesterday’s attack.

A Syrian military official who requested anonymity said yesterday that the shots were fired “during a meeting between Syrian and American officers” at a Syrian base in Palmyra.

However, a Pentagon official speaking on condition of anonymity told AFP that the attack “took place in an area where the Syrian President does not have control”.

In a statement today, the Syrian Interior Ministry said that an Isis member had “infiltrated” the meeting before carrying out the attack.

US envoy to Syria Tom Barrack said the attack only “reinforces” the US strategy to “enable capable Syrian partners ... to hunt down Isis networks, deny them safe haven, and prevent their resurgence”.

In a phone call with his US counterpart Marco Rubio, Syrian Foreign Minister Asaad al-Shaibani offered condolences and said the attack presented “a new challenge in the fight against terrorism”.

Pentagon spokesman Sean Parnell said the soldiers “were conducting a key leader engagement” in support of counter-terrorism operations when the attack occurred.

Trump called the incident “an Isis attack against the US, and Syria, in a very dangerous part of Syria”.

He said the three other US troops wounded in the incident were “doing well”.

The official Sana news agency said the attack also wounded two members of the Syrian security forces.

In an interview on state television Baba said there had been “prior warnings from the internal security command to allied forces in the desert region”.

“The international coalition forces did not take the Syrian warnings of a possible Isis infiltration into consideration,” he said.

Today, the Syrian Interior Ministry and Sana said gunmen shot dead four members of the ministry’s road security department in the northwestern Idlib province.

There was no indication whether the incident was related to yesterday’s attack.

Isis seized swathes of Syrian and Iraqi territory in 2014 during Syria’s civil war, before being territorially defeated in the country five years later.

Its fighters nonetheless still maintain a presence, particularly in Syria’s vast desert.

Last month, during Sharaa’s historic visit to Washington, Damascus formally joined the US-led global coalition against Isis.

-Agence France-Presse