Syria: Russian air strikes 'kill 12 Isis jihadists' near Raqqa but main targets are other rebelsIBTimes UK

Islamic State (Isis) militants will use "human shields" to defend their de-facto capital Raqqa as a US-backed force of Kurds and Arab fighters begin an offensive on the city, say activists. On 24 May the 30,000-strong Syrian Democratic Forces (SDF) began approaching the city from the countryside to the north.

The aim is to expel fighters from the towns and villages north of the city with the help of western air strikes from above. The umbrella SDF coalition consists of Kurdish People's Protection Units (YPG) with Arab, Christian and Turkmen militias and is thought to be a precursor for an invasion of the Daesh (Isis) stronghold at some point towards the end of the year.

Isis took the city in August 2013, just five months after it became the first Syrian provincial capital to crumble to rebel forces in the Syrian Civil War. The jihadists quickly set about enforcing their own brutal version of Sharia law before it became the capital of their self-declared caliphate in 2014.

Along with the march on Raqqa, Iraqi troops have begun an attack on the besieged city of Fallujah where thousands of civilians have tried to flee – some crawling through raw sewage. With the aid of US air strikes on the city the Iraqi military hopes to have the city completely surrounded in a few days.

"They are using the civilians as a cover. So you'll find them in the same building. In a civilian building, you'll find two or three apartments for IS fighters," said Abdel Aziz al-Hamza, a co-founder of the Raqqa is Being Slaughtered Silently group, to the AFP.

"They also talk of some schools as places to stay because these schools have basements, something underground, so they are protected from the air strikes. And they are surrounded by civilian buildings."

Russian President Vladimir Putin is said also to be preparing to help with an attack on the city with Foreign Minister Sergei Lavrov saying they are ready to co-ordinate with the SDF.

The liberation of Raqqa, which is said to be the home of between 3,000 and 5,000 jihadists, is set to be a complicated task with the jihadists dug in for defence. An estimated 50,000 civilians are believed to still be inside Raqqa with nowhere to go and a number of secret tunnels have been dug around the city to aid the insurgents.

"The civilians are besieged, they can't leave their city," said Hamza, who fled Raqqa in January 2014 and has been living in Berlin, Germany. "IS doesn't let anyone leave the city. At the same time, life has become at least ten times more expensive in the city."

The British-based Syrian Observatory for Human Rights (SOHR) monitor said there had been many coalition strikes in Raqqa on Tuesday, killing at least 22 extremists. And SDF spokesman Rojda Felat wrote on Twitter that the Raqqa assault was to "liberate northern Raqqa" and those living under IS "oppression".

SDF vs Raqqa
Fighters from the Syrian Democratic Forces (SDF) have began an offensive on RaqqaDELIL SOULEIMAN/AFP/Getty Images