DAMASCUS - Syrian rebels overran the Aleppo headquarters of the jihadist Islamic State of Iraq and al-Sham Wednesday, as claims emerged that ISIS had massacred prisoners there in cold blood.
The ISIS defeat came a day after its spokesman threatened to "crush" opposition fighters who have attacked the group in several provinces.
"There are hardly any ISIS members left in the city of Aleppo," the Syrian Observatory for Human Rights monitoring group said.
Elsewhere, a diplomat announced that two Swedish reporters missing in Syria since November had been freed.
And the fractious Syrian opposition National Coalition said it was postponing until January 17 a final decision on whether to attend peace talks in Switzerland.
On the ground, ISIS battled moderate and Islamist rebels in clashes that first erupted on Friday and have killed at least 385 people.
Announcing the new toll on Wednesday, the Observatory said it included 56 civilians.
ISIS's headquarters in a hospital in the Qadi Askar neighborhood of Aleppo was overrun by opposition fighters, who reportedly freed dozens of prisoners.
But a video posted online Wednesday claimed ISIS had previously executed at least nine prisoners after handcuffing, blindfolding and shooting them in the head.
While recording images of the bodies, the cameraman is heard to say: "This was done by ISIS. Are the victims apostates? No, they're Muslims."
ISIS spokesman Abu Mohammed al-Adnani issued a defiant message late Tuesday, urging fighters to "crush them [the rebels] totally and kill the conspiracy at birth".
"None of you will remain, and we will make of you an example to all those who think of following the same path," he added.
Adnani also warned that ISIS had "declared and begun a war" against the National Coalition and chiefs of the opposition Free Syrian Army.
"Everyone who belongs to this entity is a legitimate target for us, in all places, unless he publicly declares his rejection of that group and of fighting the mujahedeen [jihadist fighters]."
His message came hours after the head of Al-Qaeda's Syrian affiliate, Al-Nusra Front, urging an end to the fighting.
'Fighting regime a priority'
Abu Mohamed al-Jolani warned that the fighting "risks costing us dearly on the ground if it continues" and urged all fighters "to give priority to the fight against the regime".
The Nusra Front, Al-Qaeda's official affiliate in Syria, was established in mid-2011 with help from ISIS's Iraqi precursor.
The Iraqi group's chief later sought to merge with Al-Nusra, but they spurned an alliance and pledged allegiance directly to Al-Qaeda chief Ayman al-Zawahiri.
Since then, they have functioned separately, with Al-Nusra largely neutral in the latest fighting.
A security source in Damascus told AFP the infighting benefited Syria's regime, calling it a settling of scores by nations backing different rebel groups.
Regime operations continued Wednesday, with the Observatory reporting at least eight people killed in air raids on Tal Rifaat in Aleppo province.
Elsewhere, Sweden's ambassador to Lebanon and Syria confirmed that two journalists missing in Syria since November had been freed.
Swedish media named them as Niclas Hammarstroem and Magnus Falkehed.
An ICRC spokeswoman said one was taken from the Lebanese border town of Arsal to Beirut on Wednesday. Diplomats said the other was freed on Saturday.
At least 25 journalists have been killed in Syria since the conflict began in March 2011, and more than 30 are thought to be missing.
Both the regime and its opponents have been accused of abducting and killing journalists.
In Istanbul, a fiercely debated National Coalition meeting ended without a decision on attending peace talks in Switzerland on January 22.
The general assembly decided to postpone the decision until January 17.
A key Coalition member has said it will boycott the talks, and Damascus has said President Bashar al-Assad's departure will not be up for discussion.
And in The Hague, the world's chemical watchdog called for Syria to speed up handing over its arsenal for destruction, after missing a key deadline.
The joint OPCW-UN mission said Tuesday that a first cargo of chemicals had been brought to Latakia and transferred to a Danish vessel, but all Syria's most dangerous chemicals were supposed to have left the country by December 31.