Syria's opposition warned on Monday that Hezbollah's role in fighting in Homs province amounts to a "declaration of war," but the militant group said it is merely protecting Lebanese people.
The comments came as a watchdog said the Lebanese Shiite group was leading the battle in the Qusayr area of Homs, which Syrian President Bashar al-Assad has reportedly termed "the main battle" his troops are currently fighting.
"What is happening in Homs is a declaration of war against the Syrian people and the Arab League should deal with it on this basis," said George Sabra, the interim chief of the opposition National Coalition.
"The Lebanese president and the Lebanese government should realise the danger that it poses to the lives of Syrians and the future relations between the two peoples and countries," he told a news conference in Istanbul.
"We hope that the brotherly Lebanese people will raise their voices against the murder of free Syrians," said Sabra, shortly after his appointment was announced.
"We call in particular on our Shiite Lebanese brothers to stop their sons from going to kill Syrians and becoming victims of the conflict as well," he added.
Hezbollah is a close ally of the Assad regime, but has defended any involvement of its forces in Syria as a bid to protect Lebanese citizens in a string of villages inside the war-torn country.
"What Hezbollah is doing with regard to this issue is a national and moral duty in the defence of the Lebanese in border villages," Lebanon's official news agency quoted senior Hezbollah leader Sheikh Nabil Qauk as saying on Monday.
"To those who ask us to allow our brothers in these border villages to be victims of murders, kidnaps, massacres and expulsions, I respond to you: 'Can we leave these Lebanese hostage to this situation?" he added.
"Hezbollah's martyrs are the martyrs of the entire nation because they are defending their Lebanese compatriots," he said at a ceremony marking a week since the death of a Hezbollah fighter killed in Syria.
Fighting has raged in the Qusayr area of the central province of Homs for days, with regime troops winning control of a series of strategic villages in the area during the weekend.
The Syrian Observatory for Human Rights watchdog said Hezbollah forces were leading the battle in the area.
"It's Hezbollah that is leading the battle in Qusayr, with its elite forces," Observatory director Rami Abdel Rahman said.
"It's not necessarily fighters coming from Lebanon. It's Hezbollah fighters from Shiite villages on the Syrian side which are inhabited by Lebanese," he said.
The area is of strategic importance because it runs along the border with Lebanon and is near the route from Damascus to the coast.
The regime's capture of several villages in the area has raised fears among rebels that the town of Qusayr -- an opposition stronghold -- could also fall.
At the weekend, Assad himself reportedly referred to the importance of the fighting in the area, calling it "the main battle" his troops were engaged in.
"The main battle is taking place in Qusayr," the Syrian leader told a visiting Lebanese delegation, according to Abdel Rahim Mrad, a former Lebanese MP among the group.
"We want to finish it at any cost and we want to do the same in Idlib," a province on the Turkish border in the northwest which is a major rebel stronghold.
Meanwhile, Defence Minister Moshe Yaalon on Monday implicitly confirmed Israel was behind a January strike on an arms convoy in Syria, saying it had "acted" to stop advanced weaponry reaching "Hezbollah or other rogue elements".
He made the remarks at a joint news conference in Tel Aviv with visiting US Defence Secretary Chuck Hagel.
Violence across Syria on Monday killed at least 95 people, including 29 civilians, 33 rebel fighters and 33 regime soldiers, according to the Britain-based Observatory.