Tabqa airfield—home to several warplane squadrons, helicopters, tanks, artillery, and ammunition bunkers—is the third military base in the area to fall to the extremists since last month.
Those victories are part of the ISIS’s aggressive push to consolidate its hold on northern and eastern provinces, while also expanding the boundaries of its self-styled caliphate straddling the Syria-Iraq border.
The jihadists launched their long-anticipated offensive last week to seize the sprawling Tabqa facility, located some 25 miles (45 kilometers) from the extremists’ stronghold in the city of Raqqa along the Euphrates River.
After several failed efforts to breach the walls in recent days, ISIS fighters managed to punch through and storm the air base on Sunday, the Britain-based Syrian Observatory for Human Rights said. Government warplanes carried out waves of airstrikes to try to beat back the attack, but those ultimately proved unable to stem the assault.
“Some of the Syrian regime troops pulled out, and now the Islamic State is in full control of Tabqa,” said Observatory director Rami Abdulrahman. “This makes Raqqa province the first to fully fall out of government hands.”
Another activist group, the Local Coordination Committees, also said the extremist group was in control of Tabqa.
The SANA state news agency confirmed that the government had lost the air base, saying troops “are successfully reassembling after evacuating the airport.” It said that the military was still “striking terrorist groups, inflicting heavy losses on them.”
The government had made significant investments in both weapons and manpower to try to hold onto Tabqa, making its fall both a symbolic and a strategic blow.
ISIS fighters had been closing in on the base for weeks. When the fight finally came, it was bloody.
The Observatory said that at least 100 ISIS fighters were killed and another 300 wounded in the fighting, numbers that exclude casualties from the final assault. It said more than 170 government troops also were killed Sunday alone, and there were reports that another 150 may have been captured.
Tabqa is the latest in a string of bases to fall to ISIS as it strengthens its hold over a vast swath of territory in northern and eastern Syria. Last month, the extremists overran the sprawling Division 17 military base in Raqqa, killing at least 85 soldiers. Two weeks later, they seized the nearby Brigade 93 base after days of heavy fighting.
The group’s trademark brutality was on full display after those victories. They killed army commanders and pro-government militiamen, decapitating them before putting their bodies and heads on display. The Observatory reported similar acts following the fall of Tabqa on Sunday.
In the neighboring province of Deir Ezzor, ISIS fighters also have overwhelmed outposts held by Syrian rebels, systematically picking off towns and villages one by one through force and intimidation.
Their slow and steady push in northern and eastern Syria, as well as their lightning advance across Iraq, has brought under their control a stretch of territory running from Syria’s northern border with Turkey as far as the outskirts of Baghdad in central Iraq. The group has declared a self-styled caliphate in those lands to be governed under its strict interpretation of Islamic law.
Early this month, the United States began launching airstrikes against the group in northern Iraq. Those operations mark the first American military involvement in the country since the last US forces withdrew in 2011.
The mainstream Syrian opposition, which is fighting President Bashar Al-Assad as well as the Islamic State group, has called for similar air raids against the extremists in Syria. The Obama administration has so far refused, wary of getting dragged into a bloody and complex civil war that the UN says has killed more than 190,000 people.
With Tabqa now in hand, ISIS could focus on the battlefront in neighboring Aleppo province. The extremists have already captured at least a dozen towns and villages there in recent weeks, crushing mainstream Syrian rebels and advancing toward the city of Aleppo.
In the central Syrian province of Homs, however, ISIS was reportedly withdrawing its fighters after handing over its headquarters to the Al-Qaeda-linked Al-Nusra Front, the Observatory said. It did not provide a reason for the move, or more details.
The extremist group’s offensive since June has sent tremors across the region, particularly in countries that share a border with Iraq and Syria.
Also Sunday, an American held hostage in Syria by an Al-Qaeda-linked group was released, a relative and the US government said.
The US identified the freed American as Peter Theo Curtis, and said he now was safe and outside of Syria. The United Nations said it helped with the handover to UN peacekeepers in a village in the Israeli-annexed Golan Heights and that Curtis was released to American authorities after a medical checkup.
The administration provided no details about the circumstances of his abduction or his release. It was not known what prompted Curtis’ release, which comes days after militants beheaded a US journalist abducted while covering the Syrian conflict.
Meanwhile, the foreign ministers of Saudi Arabia, the United Arab Emirates, Egypt, Qatar and Jordan met in the Red Sea city of Jeddah, the official Saudi news agency said, without providing details.
But Egypt’s Foreign Ministry said ahead of the talks that the group would discuss the security threat posed by ISIS and search for ways to bring about a needed political solution to the Syrian crisis.