Lebanon's Hezbollah and the Syrian army made big advances against insurgents in the region north of Damascus on Wednesday, Hezbollah and Syrian state media said, shoring up President Bashar al-Assad's grip on a crucial border zone.
The gains in the mountainous Qalamoun region against groups including the Al Qaeda-linked Nusra Front come at a time when Assad has suffered significant defeats elsewhere, notably in Syria's northwest.
Hezbollah, an Iranian-backed Shi'ite group with a powerful militia, has been a crucial ally for Assad in the four-year-long war that has become a focal point for the struggle between Tehran and Sunni Saudi Arabia that has backed the insurgency.
Hezbollah fighters and the army seized Talat Moussa, the highest peak in the border area, the group's al-Manar TV and sources briefed on the situation said, securing control of the area.
Syrian state TV credited the advance to the army and "the Lebanese resistance," an unusual public acknowledgement of Hezbollah's role in the battle for an area used by the insurgents to ferry supplies between Syria and Lebanon.
The Syrian Observatory for Human Rights, a UK-based group that tracks the conflict, has reported that the intensity of Hezbollah's bombardment had forced many of the insurgents to withdraw.
The offensive, in areas 30 miles north of Damascus, had been expected for some time but was awaiting the end of winter. It addresses one of the risks facing Assad, who has lost control of wide parts of the north and east in the conflict estimated by the United Nations to have killed 220,000 people.
Since March, Assad has lost wide areas of Idlib province in the northwest at the border with Turkey, another supporter of the insurgency against him. He also lost the Nasib crossing with Jordan to rebels.
Islamic State, the single most powerful insurgent group in Syria, has also been launching attacks on both government- and rebel-held areas in central Syria, as it steps up efforts to expand beyond its strongholds.
Islamic State fighters killed around 30 government troops in an attack on Syrian army-held areas in Homs province overnight, the Observatory reported. At least 20 Islamic State fighters were also killed in and around the town of al-Sukhna, 190 miles northeast of Damascus.
Syrian troops repelled the attack in places and were still fighting in others, a military source said.