Residents riding motorcycles on a street as smoke rises after shelling from forces loyal to Syria's President Bashar al-Assad in Raqqa. Photo: Reuters

Syrian government forces struck Islamic State positions in and around the eastern Syrian city of Raqqa, residents said yesterday, part of a growing campaign against hardline militants who control a third of the country.

Raqqa is a major stronghold of the Islamic State, formerly known as the Islamic State in Iraq and the Levant (Isil), which took one of the Syrian army’s last outposts in the city this week to extend its gains across both Iraq and Syria.

Residents said there had been some 16 air raids yesterday on Raqqa and in nearby areas, including close to the al-Tabqamilitary base to the west of the city, a government-controlled airport that is surrounded by militants.

One attack destroyed the city’s water plant, locals said, cutting water supplies to homes and businesses.

More than 170,000 people have been killed in Syria’s three-year-old civil war, with Islamic State fighters gaining momentum in recent weeks, boosted by equipment seized in a rapid offensive in neighbouring Iraq. In response, the Syrian army has become more aggressive, using air strikes to attack their positions.

“The bombardment increases then falls off, but when they are not bombing al-Tabqa airport they are bombing the surrounding towns or bombing Raqqa. The sound of aircraft is constant,” a Raqqa resident said, asking to remain anonymous to protect his identity.

Civilian casualties have been kept to a minimum because many residents have fled to nearby villages and rural areas

Locals in Raqqa say civilian casualties have been kept to a minimum because many residents have fled to nearby villages and rural areas, while those remaining spend their days in shelters.

The Islamic State’s Syria headquarters are situated in what used to be Raqqa’s municipality buildings in densely populated civilian areas.

“It is these buildings that are now targeted in the air raids,” said an opposition activist living in the city, who opposes both the Islamic State and the government. He said that the air force was now using Russian-made Sukhoi bombers, which carry bigger munitions than MiG fighter jets.

Until this summer, President Bashar al-Assad’s forces held off from targeting the al- Qaeda offshoot, allowing the group to thrive, while weakening less hardline opposition groups that are backed by the West.

Assad has long painted the uprising in Syria as a foreign-backed Islamist conspiracy and his enemies say he has allowed the Islamic State to grow to promote that idea.

Damascus has not commented on why it was now focussing on Islamic State fighters rather that other rebel groups.

The Syrian Observatory for Human Rights, which has tracked violence on all sides of the conflict that began in March 2011, said government forces and Islamic State fighters fought in two villages in Raqqa province on Monday, al-Ajeel and al-Khazaneh near the Tabqa airport.

The conflict in Syria started when Assad cracked down on a pro-democracy uprising, which then armed itself. The war pits overwhelmingly Sunni Muslim rebels against Assad, a member of the Shi’ite-derived Alawite minority, backed by Shi’ite militias from Iraq and Lebanon.