Hezbollah chief Hassan Nasrallah said Sunday that Syria's regime and the "resistance axis" including his Lebanese Shiite militant group would triumph in the Syrian conflict.
Speaking as Lebanon entered a presidential vacuum, Nasrallah also said his Shiite movement wants the country to have a president "who does not conspire against it."
"Syria will triumph and the resistance axis will triumph," Nasrallah said in a televised address to mark the 14th anniversary of Israel's withdrawal from south Lebanon.
Hezbollah has sent thousands of fighters into Syria to support President Bashar al-Assad's forces against rebels seeking his overthrow, saying they are defending an "axis of resistance" against Israel and the West.
"The project that targeted Syria and the region has been forced back to a great extent, and has suffered several defeats. Numerous factors contributed to this, some local, and others regional and international," said Nasrallah.
In recent months, Syria's army backed by Hezbollah, Iraqi Shiite fighters and pro-regime militia has scored a series of advances in its bid to crush the rebellion.
Hezbollah, its chief said, is fighting in Syria because Damascus "nourished and protected the Lebanese resistance. This is the Syria we are defending."
Nasrallah meanwhile described Western backing for rebels seeking Assad's overthrow as a "historic sin."
His speech came two weeks ahead of a presidential vote in Syria that is widely expected to return Assad to power.
"Syria is advancing towards a presidential election that no amount of foreign intimidation or mockery by those who call themselves the 'Friends of Syria' can block or stop," he said.
The exiled opposition and its Western backers, who have held several international meetings under a "Friends of Syria" umbrella, have ridiculed the June 3 vote as a "farce".
Syria's civil war raging since March 2011 has killed more than 160,000 people and forced nearly half the population to flee their homes.
More than a million Syrians have taken refuge in neighbouring Lebanon, which has been sharply divided into pro- and anti-Assad camps.
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The war has also spilled across its borders.
Syria dominated Lebanon for 30 years until 2005, but continues to exert influence over the tiny Mediterranean country through its allies.
- Israel warning -
Hezbollah, Nasrallah said, is still able to deter its arch-enemy Israel, against which it fought a 33-day war in 2006 that killed 1,200 Lebanese, mostly civilians, and 160 Israelis, mostly soldiers.
"Despite the developments and events that are taking place in our region, especially in Syria, the resistance (Hezbollah) still has the capacity to deter Israel," he said.
"This is one of the Israeli enemy's concerns. It looks at Syria and (key Assad and Hezbollah backer) Iran ... and sees that they are giving all the help they can to the resistance," he said, suggesting Hezbollah is still receiving military and financial support from its allies.
Nasrallah also warned that Hezbollah will respond if Israel carries out any attacks in the border region.
"Should we reach the point where the resistance must respond, the resistance will not be silent," he said.
His televised speech was followed by a large crowd that gathered in the southern Lebanese town of Bint Jbeil.
It came a day after Lebanon's ex-president Michel Sleiman left the presidential palace at the end of his mandate, as a vacuum opened up because of a deep political rift between rival blocs.
Nasrallah said the movement is "looking forward to choosing a president who does not conspire against it."
Hezbollah had criticised Sleiman for his position that weapons should be in the hands of the Lebanese army, and for calling on the movement to withdraw from Syria.
Hezbollah says it maintains its huge arsenal to fight Israel.