Hezbollah chief Hassan Nasrallah on Saturday vowed "victory" in Syria, where militants of his powerful Lebanese Shiite movement are fighting alongside regular troops against rebels trying to topple the regime.
"I say to all the honourable people, to the mujahedeen, to the heroes: I have always promised you a victory and now I pledge to you a new one" in Syria, he said at a ceremony marking the 13th anniversary of Israel's military withdrawal from Lebanon.
Nasrallah said Hezbollah would always stand by its ally, President Bashar al-Assad, and his regime, stressing that its own interests were at stake.
"We will continue along the road... bear the responsibilities and the sacrifices," he said in a video link of a speech delivered live on a huge screen.
"This battle is ours... and I promise you victory," he said.
"Syria is the rear guard of the resistance (Hezbollah's fight with Israel), its backbone, and the resistance cannot stay with its arms folded when its rear guard is exposed.
"We are idiots if we do not act," said Nasrallah who avoids appearing in public for fear of being assassinated by Israel.
The intervention of hundreds of Hezbollah fighters has given Assad the upper hand in Qusayr, a strategic central town in Syria across the border with Lebanon, that had been in rebel hands.
Syrian forces launched an assault on Qusayr on Sunday but are still meeting with fierce resistance from the rebels, as the town provides an important supply line for arms and volunteers from nearby Lebanon.
Qusayr is a key prize for Assad's forces because of its strategic location between Damascus and the Mediterranean coast, the Alawite heartland of the embattled president's regime.
Nasrallah ruled out any alliance with the mostly Sunni Muslim rebels battling the Syrian regime.
"Hezbollah cannot be in the same trench as the United States, Israel, the takfiris (radical Muslims)... who disembowel, behead and desecrate tombs," he said of reports that rebels had vandalised the shrine of a venerated Shiite saint.
Nasrallah also appealed for the anti- and pro-Syrian camps in Lebanon to avoid the violence in the northern port city of Tripoli that has cost 30 lives over the past week.
"We call again for Lebanon to be left out of any confrontation. We are opposed over Syria? You want to fight in Syria? Let's fight there but preserve the neutrality of Lebanon. Why should we fight in Lebanon?" he asked.
He also downplayed a proposal by France for the European Union to include Hezbollah's militia on a blacklist of terrorist groups.
"We have been on the list of terrorist organisations for a long time, and that is just ink on paper and changes nothing. You can boil your list and drink it."
Hezbollah is already blacklisted by Australia, Britain, Canada, Israel, the Netherlands and the United States.
Saturday marked the 13th anniversary of Israel's withdrawal from south Lebanon after 22 years of occupation, in a move widely credited to Hezbollah's constant attack on Israeli forces.