The extremist group Islamic State has launched a series of attacks across Syria, using military equipment seized from Iraq in its biggest concerted challenge yet to Assad regime forces.
Fighters from Islamic State (Isis) have attacked two military bases in the northeast of the country and regime-held areas near Aleppo.
They seized most of one base before coming under retaliatory aerial bombardment, seizing senior regime officers and in at least one case decapitating him, placing his easily recognisable head on a pole, according to pictures posted on social media.
The attacks mark a significant shift in the Syrian civil war. While the regime and Islamic State have fought in the past, both have until now preferred to focus their energies on the third force in the civil war, the so-called "moderate rebels" comprising the Free Syrian Army and a variety of Islamist groups.
The attacks also suggest the group has, for now, abandoned plans to move further into Iraq or attack the capital Baghdad.
The change of tactics by Islamic State follows the gradual weakening of the Western-backed rebels, who are squeezed between the jihadists and the regime.
They declared war on the Islamic State in January, hoping that tackling the extremists would encourage more military backing from the West and its allies.
That backing never came, and with thousands of opposition fighters dying in the battles between competing rebel forces, the regime has advanced across key battlegrounds in the centre and north of the country, including Aleppo.
Meanwhile, in a series of lightning raids and defections, Islamic State managed to drive out competitors from most of the eastern province of Deir al Zour, and seized oilfields from the regime. On Thursday, they attacked two of the remaining regime strongholds in the region, the Division 17 base east of Raqqa, and the Battalion 111 base further north in Raqqa, according to activists and the Syrian Observatory for Human Rights.
State media said that the attack on Battalion 111 base had been resisted. However, the jihadists took most or all of Division 17, according to conflicting accounts. Among those killed were the head of Raqqa intelligence for the regime.
Islamic State has been emboldened by the success of its sweep into Iraq, where it captured Mosul.