Islamic State (IS) militants have retaken a strategically important town in northern Syria from rebel forces, activists and the jihadist group say.
The Syrian Observatory for Human Rights reported that al-Rai was overrun early on Monday after intense fighting.
Al-Rai is close to the border with Turkey and is a key supply route into IS-held territory in Aleppo province.
IS had lost the town last week in an assault by rebels fighting under the banner of the Free Syrian Army (FSA).
The jihadist group controls a large swathe of territory across northern Syria, but has been pushed back in a number of areas in recent months by rebels, Kurdish fighters and Syrian government forces.
Al-Nusra 'launches offensives'
Since the end of March, rebel factions backed by Turkey have seized more than a dozen IS-held villages along the Syrian-Turkish border.
On Thursday, they captured al-Rai after a two-day battle with militants in the town, and threatened to push on towards the nearby IS strongholds of Dabiq and al-Bab.
But four days later, IS was able to regain control of al-Rai and six villages to the west, according to the Syrian Observatory (SOHR), a UK-based monitoring group, and the Local Co-ordination Committees (LCC), an opposition activist network.
IS also issued a statement confirming it had driven rebels out of al-Rai.
"The fact that the rebels could not hold on to al-Rai shows that it is impossible to maintain an advance against IS without adequate air cover," the Syrian Observatory's director, Rami Abdul Rahman, told the AFP news agency.
The SOHR also reported that rival jihadists from the al-Qaeda-affiliated al-Nusra Front and allied rebels had launched offensives in Aleppo, Hama and Latakia provinces on Monday. So far, they had seized a hilltop in Latakia, the heartland of President Bashar al-Assad's Alawite sect, it added.
"This is the offensive that al-Nusra warned it would carry out several weeks ago," Mr Abdul Rahman said, referring to a threat issued by the group when Russia announced it was withdrawing most of its forces from Syria, after a six-month air campaign against Mr Assad's opponents.
A Syrian military source told AFP that armed groups were trying to attack military positions in Latakia and Hama, but had not succeeded in making any advances.
Neither IS nor al-Nusra are included in a cessation of hostilities brokered by the US and Russia that has largely held since taking effect on 27 February.
Later this week, representatives of the government and opposition are due to participate in a new round of UN-brokered talks in Geneva aimed at ending the five-year conflict in Syria, which has left more than 250,000 people dead.