A resident of Tabqa city touring the streets on a motorcycle waves an Islamist flag in celebration after Islamic State militants took over Tabqa air base, in nearby Raqqa city August 24, 2014. I
A resident of Tabqa city touring the streets on a motorcycle waves an Islamist flag in celebration after Islamic State militants took over Tabqa air base, near Raqqa city August 24, 2014.Reuters

In an incident that dealt a heavy blow to the Assad regime, Islamic State stormed an air base in northeast Syria on Sunday, capturing it from the government forces.

The militants taking over the Tabqa air base near Raqqa city comes as further evidence that the Sunni extremist group is determined to widen its grip on the region, in their quest to enlarge and establish their caliphate.

Reuters, citing Syrian observatory for human rights, reported that at least 346 Islamic State fighters were killed and over 170 soldiers died since Tuesday in the fight that has been raging over the Tabqa base, making it one of the deadliest confrontations between the two groups since the war commenced.

Reports suggest that fighting intensified on Sunday inside the air base, which was the Syrian army's only foothold in an area otherwise controlled by the jihadist group. Islamic State has claimed major swathes of Iraqi and Syrian land ever since it started its bloody campaign.

Celebratory gunfire was heard as several mosques announced through loudspeakers that the air base was taken by IS. Militants also displayed the severed heads of Syrian soldiers in the city square, according to witnesses.

Syrian news agencies on Sunday conceded the loss of the air base in reports which were noted to have used euphemistic terms. For instance, instead of saying that they lost the base, the reports focused on the Syrian forces performing "a successful regrouping after evacuating" the base.

The Syrian observatory for human rights also noted that Islamic State has trapped around 150 soldiers in an area near the airport and is believed to be holding them captives.

Television footage showed the government forces trying to defend the base. Many jihadist fighters were killed as Syrian warplanes pounded the area, the observatory added.

The capture of the Tabqa air base comes at a time when US President Barack Obama is considering air strikes Islamic State's bases in Syria, as the battle against the Sunni militant group is likely to take a new turn with an aggressive American assault being planned.