Militants with the Al Qaeda breakaway group Islamic State seized control of a military base in northern Syria late Thursday night, beheading dozens of soldiers and displaying their headless bodies, activists said.
It is only the latest victory for the extremist group that has made rapid advances in both Iraq and Syria in recent months as it pursues its goal of creating an Islamic caliphate.
There have been sporadic skirmishes around the base, called Division 17, in Raqqa province for months, but on Wednesday Islamic State fighters launched a concerted offensive. The fighting began when two militants blew themselves up in with suicide car bombs near the base's chemistry battalion, according to the Syrian Observatory for Human Rights, a pro-opposition watchdog group based in Britain.
Within a day the militants had taken over the base and begun carting off light and heavy weaponry, said Abu Muhammad, an activist with the Masar Press Agency.
"Every government soldier they capture they execute immediately," he said.
The assault on Syrian government positions marks a departure for the Islamic State, which recently shortened its name from the Islamic State of Iraq and Syria once it declared that it had succeeded in forming the caliphate. Until recently it had for the most part not fought regime forces, instead focusing on seizing territory from opposition rebels who are fighting to oust the government of Syrian President Bashar Assad.
The lack of open conflict between the Islamic State and the government, avowed enemies, had led many in the opposition to believe the two sides were colluding to undermine and defeat other rebel forces.
When the Islamic State, which grew from Al Qaeda's Iraqi branch, first entered the Syrian conflict last year, it fought alongside other rebel forces. But soon it turned against others in the opposition, accusing them of corruption, executing their fighters and activists and pushing them out of towns and villages. As the Islamic State increasingly fought with rebels, the opposition found it harder to maintain its battle against government forces and lost control of many areas.
But as the Islamic State has expanded into neighboring Iraq, where it shares control over about half the country, and consolidated its hold on major parts of eastern Syria, it has launched offensives against regime targets as part of its greater plan to establish the Islamic caliphate in both countries and beyond.
The Islamic State now holds about a third of Syria, according to the observatory.
Last week the militant fighters seized the Sha'er gas field from regime and paramilitary forces in the central Homs province. The move struck a major blow against the government, which had already lost control over many oil fields in eastern Syria. Islamic State controls most of the fields, making it among the wealthiest terrorist networks, experts believe.
The Islamic State executed or otherwise killed 270 paramilitary fighters, guards and employees at the Sha'er field, the observatory said.
State media did not acknowledge the loss of Division 17, but reported that soldiers defending the base were deployed to face the Islamic State in the nearby city of Raqqa.
Activists reported that government warplanes were carrying out airstrikes around the base on Friday.
The Islamic State has also sent its fighters to attack the last two remaining government positions in the province, a military airport and Brigade 93 on the Turkish border, in order to consolidate control over the entire province, said Abu Muhammad, the activist.
"That's what we're hearing from their fighters," he said.