Forces loyal to Syrian President Bashar al-Assad have reportedly retaken a key town to the south of the capital Damascus.
The Syrian Observatory for Human Rights said that the Syrian army seized control of the town of Bweida with the help of foreign fighters from Iraq and Lebanon.
The push appears to be part of a concerted effort by regime forces to dislodge rebels from areas of Damascus under their control.
"The army's advance is part of an attempt to crush the rebels' positions in the countryside south of Damascus, in order to isolate those operating within the southern belt of the capital," said the Observatory's director Abdel Rahman.
Foreign fighters involved in the operation included Iraqi volunteers from the Shia Abul Fadl al-Abbas brigades - part of a network of Shia paramilitary groups set up to supplement the regime's overstretched regular forces - as well as Hezbollah fighters.
The strategic town lies close to the shrine of Sayyida Zeinab, a granddaughter of Muhammed, which is revered by Shiites around the world.
Clashes continued closer to the shrine on Wednesday, according to reports.
The apparent threat to the shrine by Sunni Islamists, who see Shia Islam and its symbols as heresy, has been one of the main recruiting tools of pro-regime militias among Iraqi and Lebanese Shia Muslims.
Fighters from both sides of the Sunni-Shia divide have been streaming across Syria's border's to join opposing sides of the ongoing conflict there, which has killed well over 100,000 people. The rebel movement is made up primarily of Sunni Muslims, while the regime counts mainly on the support of Shia Muslims and members of President Assad's Allawite sect, an offshoot of Shia Islam.
Hezbollah, an Iranian-backed terrorist group initially founded to fight Israel, has proved a key ally in the Assad regime's battle against rebel forces, providing crucial support against rebels in the strategically-important Al Qusair region near the Lebanese border, as well as around the cities of Homs and Aleppo.
But pressure at home recently led the group's leader, Hassan Nasrallah, to announce that he would be withdrawing 1,200 fighters from Syria.
The group - which once enjoyed support from across the Muslim world - has seen its popularity plummet, particularly among the Sunni Muslim world, due to its support for the Assad regime.
Recent attacks on Shia Muslim strongholds in Lebanon, apparently carried out in revenge for Hezbollah’s support for Assad, have also angered many Shi'ite Lebanese, and with many of Hezbollah’s combatants stationed in Syria the group has found itself increasingly unable to secure its traditional supporters at home.
According to the reports, the Hezbollah troops returning to Lebanon will not immediately resume their old positions near Israel’s northern border, but may be stationed across Lebanon instead, possibly in an attempt to reconsolidate the group's grip over its traditional strongholds.
However, it was also reported that many Hezbollah troops will still remain in Syria, including 550 who were recently sent to the Damascus area and were likely involved in the recent fighting at Bweida.
Those who have been called back to Lebanon will apparently be replaced by Iranian “volunteers” from the ranks of the Revolutionary Guards, reports say, as part of the increasingly direct involvement of Iranian troops fighting on the ground in Syria on behalf of Assad.