BEIRUT -- Islamic extremists fired rockets and tank shells Wednesday at a major air base in northeastern Syria, kicking off a long-anticipated offensive to seize the last position held by the Syrian government in a province that is a stronghold of the Islamic State group, activists said.
The attack on the Tabqa air base had been expected for weeks. Islamic State fighters have tightened their siege of the sprawling facility in recent days, capturing a string of nearby villages.
The group in recent months has virtually eliminated the presence of President Bashar Assad's military in Raqqa province, with the exception of Tabqa. The air base is one of the most significant government military facilities in the area, containing several warplane squadrons, helicopters, tanks, artillery and ammunition.
Last month, Islamic State fighters overran the sprawling Division 17 military base in Raqqa, killing at least 85 soldiers. Two weeks later, the extremists seized the nearby Brigade 93 base after days of heavy fighting.
Militant websites affiliated with the Islamic State announced the assault Wednesday. Since July, following their blitz across Iraq and after they declared a self-styled caliphate straddling the Iraq-Syria border, Islamic State fighters have methodically picked off isolated government bases in northern and eastern Syria, killing and decapitating army commanders and pro-government militiamen.
The Tabqa attack also was reported by the Britain-based Syrian Observatory for Human Rights and the Raqqa Media Center, an activist collective, which reported fierce clashes around the facility accompanied by government airstrikes.
Both activist groups said army warplanes conducted airstrikes on suspected militant positions in the nearby town of Tabqa on the Euphrates river, which flows from Turkey through Syria into Iraq. The Observatory said at least six Islamic State fighters were killed.
The town is home to al-Furat dam, Syria's largest, now controlled by the Islamic State group.
The group's lightning advance across Iraq, as well as its slow and steady push in northern and eastern Syria, has brought under its control territory stretching from Syria's northern border with Turkey as far as the outskirts of Baghdad in central Iraq. The militant gains brought U.S. forces back into conflict in Iraq for the first time since they withdrew in 2011. Washington began conducting airstrikes against the Islamic State group in Iraq on Aug. 8.
On Tuesday, militants released a video showing the beheading of American journalist James Foley in what the extremists called retribution for the U.S. aerial campaign in Iraq. The militants threatened to kill another captive they also identified as an American journalist.
The beheading marks the first time the Islamic State has killed an American citizen since the Syrian conflict broke out in March 2011, upping the stakes in an increasingly chaotic and multilayered war. The killing could complicate U.S. involvement in Iraq, and the Obama administration's efforts to contain the group as it expands in both Iraq and Syria.
In Washington, a U.S. official said American fighter jets and drones have conducted nearly a dozen airstrikes since Tuesday, including in the hours after the Foley video was released. The official was not authorized to discuss the ongoing operations publicly and spoke on condition of anonymity.
The main Western-backed Syrian opposition group condemned Foley's killing, and sent its condolences to his family and friends.
Dr. Najib Ghadibian, the Syrian National Coalition's special representative to the U.S., called Foley "a brave journalist who worked tirelessly to show the world the suffering of the Syrian people and the Assad regime's brutality."
Associated Press writer Lolita C. Baldor in Washington contributed to this report.
