Barack Obama has said that the participation of five Arab nations in airs raids against ISIL in Syria "makes it clear to the world this is not America's fight alone".

The US president on Tuesday promised to continue the fight, which he said was vital to the security of his country, the Middle East and the world.

"Once again, it must be clear to anyone who would plot against America and do Americans harm that we will not tolerate safe havens for terrorists who threaten our people," he said.

He added the joint fight against ISIL would take time, and promised to build more international support for the effort.

He said the US was proud to stand shoulder-to-shoulder with Bahrain, Qatar, Saudi Arabia, Jordan and the UAE in conducting the attacks.

The US-led military coalition launched the raids early on Tuesday against ISIL positions in northern and eastern Syria.

The raids also hit al-Qaeda's branch in Syria, known as the Nusra Front, which has fought against ISIL. Washington considers it a terrorist group that threatens the US.

Syria's foreign ministry said Washington told Damascus of the raids shortly before they began. 

John Kirby, the spokesman for the US defence department, said on Tuesday that more than 160 munitions were fired on ISIL targets in Syria. He said that the US had no indication so far that any civilians were killed, but that assessments were under way.

The US and five Arab countries began their raids at about 3am Syrian time on Tuesday.

Jordan, Bahrain and the UAE said their air forces were involved.

Jordan said it would "not hesitate to take further actions to target and kill terrorists who are trying to attack our country".

The strikes hit ISIL's training compounds and command centres, storage facilities and vehicles in its de facto capital Raqqa, and targets in Deir ez-Zour, Abu Kamal and Hasaka, according to US officials.

The UK-based Syrian Observatory for Human Rights reported that at least 70 ISIL fighters were killed and more than 300 wounded in Raqqa and the east. 

Rami Abdurrahman, the head of the Observatory, said about 22 raids targeted Raqqa province in addition to 30 in Deir ez-Zour. A military air base in the town of Tabqa and the town of Tel Abyad on the border with Turkey were also targeted, the Observatory said.

Further west, the strikes hit the village of Kfar Derian, a Nusra Front stronghold.

Around a dozen Nusra Front fighters were killed as well as 10 civilians, according to two activists based in nearby Aleppo, Mohammed al-Dughaim and Abu Raed. One of the group's best snipers, known as Abu Youssef al-Turki, was among those killed, al-Dughaim said.