Raqqa assault: US-backed Syrian rebels launch attack to liberate Isis stronghold

The US-backed campaign to capture Isis’ de facto capital of Raqqa in Syria has officially started, the Syrian Democratic Forces (SDF) has announced, marking the beginning of the end of the so-called caliphate.

The three-fronted attack was launched from the north, east and west of the city on Monday, spokesperson Talal Sillo told Reuters by telephone on Tuesday. Troops have already managed to enter the city's eastern gate.

Isis took advantage of the chaos of Syria's complex war to seize territory and sweep into neighbouring Iraq in 2014, imposing its extremist beliefs and brutal rule on civilians since.

The Kurdish-Arab SDF coalition of ground fighters has been slowly tightening the siege around jihadi militants in the northern city of Raqqa since November, assisted by US-led coalition air strikes.

In May, the SDF captured the nearby town and dam of Tabqa after Isis fighters reportedly agreed to surrender, retreating to Raqqa, the sole remaining stronghold in the area.

The Pentagon confirmed last week that shipments of arms including AK-47s and small calibre machine guns as well as vehicles and ammunition were on their way to the SDF ahead of the battle for the city.

Despite initial indications he was willing to work with Syrian President Bashar al-Assad to defeat Isis, US President Donald Trump has doubled down on the policy of his predecessor Barack Obama, backing the SDF and other Kurdish fighters instead.

Syria's Kurdish militias are the most effective ground force against the jihadist movement, although continued US support has angered Nato ally Turkey, which views them as terrorists. Prime Minister Binali Yildirim said on Tuesday that Ankara "would not hesitate to retaliate" if the US-backed operation posed any threat to Turkey.

The Kurds have been helped by international coalition bombing since 2014, although rights groups such as Amnesty International have consistently criticised the US-led air strikes for causing unnecessary loss of human life.

UK-based war monitor Syrian Observatory for Human Rights said that at least 21 civilians had been killed - likely by bombing - as they fled intense fighting in Raqqa on Monday night.

Operation Euphrates Wrath - as the campaign is known - is designed to dovetail with the fight to liberate the city of Mosul from Isis in neighbouring Iraq.

Mosul, once the largest city under Isis' control, is about to fall to Iraqi coalition forces after eight months of bitter street-by-street warfare. SDF forces hope to cut off the last fighters fleeing west over the border before they reach Raqqa.

The loss of both cities will effectively spell the end of Isis' so-called caliphate, although it is unlikely the militants will go quietly in their final battle.

Observers expect the jihadi organisation to mount a full-scale insurgency in both Syria and Iraq after it ceases to be a land-holding force in the two countries, and to step up terror attacks around the world.