By Delil Souleiman with Sarah Benhaida in Mosul
US-backed Kurdish-Arab forces launched an offensive Sunday on the Islamic State group's de facto Syrian capital Raqa, upping pressure on the jihadists who are already battling Iraqi troops in Mosul.
The start of the assault by the Syrian Democratic Forces (SDF) came as Iraqi forces fought inside Mosul for the third day running amid fierce jihadist resistance.
The two cities are the last major urban centres under IS control after the jihadists suffered a string of territorial losses in Iraq and Syria over the past year.
The US-led coalition battling IS is backing both assaults, hoping to deal a knockout blow to the self-styled "caliphate" it declared in mid-2014.
SDF commanders announced the start of the Raqa operation in Ain Issa, some 50 kilometres (30 miles) north of the city.
"The major battle to liberate Raqa and its surroundings has begun," SDF spokeswoman Jihan Sheikh Ahmed said.
Operation "Wrath of the Euphrates" involves some 30,000 fighters and began on Saturday night, Ahmed said.
SDF forces are advancing on three fronts, from Ain Issa and Tal Abyad to the north of Raqa, and from the village of Makman to the east.
SDF spokesman Talal Sello told AFP forces would first seize areas around Raqa before taking the city itself.
"The fight will not be easy, and will require accurate and careful operations because IS will defend its bastion knowing that the loss of Raqa will mean it is finished in Syria," Sello said.
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