A US helicopter raid on Monday (April 17) targeted a senior "Islamic State of Iraq and Syria" (ISIS) leader in Syria who is suspected of plotting terror attacks in Europe and the Middle East.

The US military's Central Command (CENTCOM) said its forces "conducted a unilateral helicopter raid in northern Syria in the early morning ... targeting a senior ISIS Syria leader and operational planner".

The target of the strike was "responsible for planning terror attacks in the Middle East and Europe", it said.

"The raid resulted in the probable death of the targeted individual" while "two other armed individuals were killed", the statement said, without identifying any of them.

The Syrian Observatory for Human Rights said the strike "targeted the building where an ISIS member was present" in a village about 25km west of Jarablus on Syria's northern border with Turkey.

The Observatory said the main target was arrested, while the strike killed two other fighters.

The ISIS leader had reportedly taken refuge in the area a month earlier, according to the Observatory.

US forces have carried out a series of raids in recent months targeting ISIS leaders and operatives in Syria and Iraq.

In an April 8 helicopter raid in eastern Syria, CENTCOM forces captured an ISIS attack facilitator it named as Hudayfah al-Yemeni, along with two associates.

On April 3, the US military said it had launched a strike in Syria killing senior ISIS leader Khalid Aydd Ahmad al-Jabouri, who CENTCOM said was responsible for planning attacks in Turkey and Europe.

Helicopter-borne US troops working with the Syrian Democratic Forces (SDF) on February 18 captured an ISIS provincial official in Syria the US military identified as "Batar", who had been involved in planning attacks on detention centres.

The capture came a day after a senior ISIS leader in northeastern Syria, identified as Hamza al-Homsi, was killed in a separate US/SDF helicopter raid.

Some 900 US troops remain in Syria, most in the Kurdish-administered northeast, as part of the international coalition battling remnants of ISIS, which remains active in both Syria and neighbouring Iraq.

The group's remnants operate out of hideouts in desert and mountain areas.

ISIS "remains able to conduct operations within the region with a desire to strike beyond the Middle East", CENTCOM chief Gen. Michael "Erik" Kurilla said Monday.

Attacks blamed on ISIS kill at least 41

In separate attacks on Sunday, suspected ISIS fighters killed at least 36 truffle hunters and five shepherds in Syria, the Observatory said, with 17 pro-regime fighters among the dead.

Observatory head Rami Abdel Rahman said the extremists "killed 36 people on Sunday while they were collecting truffles in the desert east of Hama (city)".

The Observatory said extremist elements riding motorbikes also attacked a group of shepherds in Deir Ezzor province, killing five and seizing their livestock.

Two other shepherds were kidnapped, it said.

Syrian state media also reported five dead in the attack, and said the group of extremists had opened fire on the animals, killing 250 sheep.

Also in Deir Ezzor, the decomposed bodies of two civilians thought to have been truffle hunters killed days earlier by extremists were recovered, the Observatory said.

Since February, more than 240 people have been killed in ISIS attacks targeting truffle hunters or by landmines left by the extremists, the Observatory said.

The victims included 15 people foraging for truffles who had their throats slit by ISIS last month.

In February, ISIS fighters on motorcycles opened fire on truffle hunters and killed at least 68 people, the Observatory said at the time.