The Kurdish-led Syrian Democratic Forces (SDF) captured several frontline villages and farms about 45 kilometres north of al-Raqqa, while warplanes buzzed the area and targeted terrorists positions, the Syrian Observatory for Human Rights said.

Daesh, via its Amaq Agency media outlet, claimed to have killed 14 Kurdish fighters in a suicide car bomb attack on a checkpoint in the area.

The Kurds said they had destroyed two car bombs, but a source close to the SDF, who asked not to be quoted by name, said that an unspecified number of SDF fighters had been killed in the attack.

Hours earlier, SDF commanders announced the move on al-Raqqa - which comes as Iraqi forces push into the organization's Iraqi stronghold of Mosul - and said it was being conducted in coordination with the US-led air coalition against Islamic State.

Around 80 per cent of those participating in the so-called Euphrates Anger operation are civilians from Al Raqqa, the commanders added.

The Kurdish lead in the battle for mainly Arab Raqqa may be a flashpoint both for local residents and for neighbouring Turkey, a fierce opponent of the Syrian Kurds which itself hopes to play a role in capturing the north-eastern city.

"We confirm... that the Euphrates Anger operation will move firmly until it achieves its aim of isolating and then bringing down the capital of global terrorism," an SDF spokeswoman said.

"We call on our steadfast people [in al-Raqqa] to steer clear of the enemy 's positions that will be the target of fire from the liberation forces and alliance," spokeswoman Jihan Sheikh Ahmed, clad in combat fatigues, said at a press conference in Ein Issa near the front lines.

Al-Raqqa in north-eastern Syria has been under Daesh control since 2014.

The SDF includes Arabs and other ethnic groups, but it is effectively led by the powerful Kurdish People's Protection Units, who have seized swathes of northern Syria from Daesh since defeating the extremist militants in the border town of Kobane early last year.

SA - 12