Islamic State supporters celebrate capture of
Islamic State supporters celebrate capture of Reuters

Jihadi forces from the Islamic State organization have seized a military airport which was the last remaining Syrian army outpost in the country's northern Raqqa province, capturing heavy weapons including missiles, tanks, artillery batteries, helicopters and warplanes.

Tabqa airbase fell Sunday night after days of fighting claimed the lives of approximately 500 Syrian soldiers and Islamic State fighters, according to the Syrian Observatory for Human Rights. The Observatory claimed a further 150 soldiers were trapped in a position nearby the base and were effectively being held captive by the Islamists.

The Syrian military attempted to put a positive spin on the defeat by claiming its forces had conducted a "successful evacuation operation" of the base, and added planes were bombing the airbase following its capture.

But pictures shared on social media show grinning Islamic State fighters displaying captured weaponry and standing atop captured MiG fighter jets.

Islamic State fighters parade captured aircraft, dead soldiers in Taqba base:

The Syrian regime had sent reinforcements to the embattled base on Friday night, and as late as Saturday Syrian State TV was broadcasting footage from inside the base, showing loyalist forces in full control.

The fall of the base is a serious strategic blow for the Assad regime, which had used it to bomb both the Islamic State in the north as well as other rebel groups to the south. The Islamic State now has full control over Raqqa Province and roughly a third of northern and eastern Syria in total, as well as vast swathes of northern Iraq.

Meanwhile, IS withdrew from a part of the city of Homs previously under its control in the face of a concerted assault by rival rebel forces, led by Al Qaeda's official branch in Syria, the Nusra Front. IS and the Nusra Front have been engaged in an increasingly bloody rivalry in Syria, after IS's (then ISIS) broke away from Al Qaeda in 2013.

IS has also been involved in a prolonged battle with other rebel groups elsewhere in the country.