Hezbollah chief Hassan Nasrallah vowed on Thursday to keep his forces in Syria fighting alongside President Bashar al-Assad's regime, in a rare public speech delivered in Beirut.
Nasrallah, who normally appears via video link for fear of assassination by Israel, spoke in Hezbollah's south Beirut stronghold as tens of thousands of followers of his Shiite militant group marked Ashura, one of the holiest days of their faith.
"We have said on several occasions that the presence of our soldiers on Syrian soil is to defend... Syria, which supports the resistance" against Israel, Nasrallah said.
"So long as that reason exists, our presence there is justified.
"Those who speak of our withdrawal from Syria as a condition to form a government in Lebanon know that it is an impossible condition.
"We won't negotiate on the existence of Syria (in exchange for) a handful of ministries."
Lebanon has been without a government for seven months due to deep divisions between Hezbollah and parties opposed to its military action in neighbouring Syria.
The powerful Shiite movement says its fight alongside the Assad regime is aimed at combatting Sunni extremists who are targeting Syria's Shiite and Christian minorities.
But it has stirred sectarian tensions in Lebanon, where many Sunnis back the Syrian uprising.
Nasrallah also insisted his movement would keep its weapons, despite longstanding calls to lay them down.
"On this day of Ashura, I declare our commitment to the resistance with its readiness, its resources, its weapons... as essential to protect our country and our people," he said.
Nasrallah's address came at the climax of rituals for Ashura, a festival that marks the killing of Hussein, grandson of the Prophet Mohammed, at the hands of soldiers of the caliph Yazid in 680 AD, an event that lies at the heart of Islam's sectarian divide.
Men and women dressed in black flooded the streets of Beirut's mainly Shiite southern suburbs to observe the solemn mourning that tradition dictates.
Security was tight after multiple attacks against the Hezbollah stronghold, including car bombs on July 9 and August 15 that killed 27 people.
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The Lebanese army deployed armed personnel carriers and troops at checkpoints, and Hezbollah security forces manned their own checkpoints with men and women searched separately as they entered.
The day began with prayers and a recounting of the story of Imam Hussein, broadcast over loudspeakers to rows of men and women seated separately on white tarpaulins laid on the street.
As the narrator described Hussein's death, men and women wept loudly, and volunteers moved through the crowd passing out tissues.
Shiite faithful from all walks of life participated.
Many women were draped in the Iranian-style chador veil but others participated with their hair uncovered, and men sported everything from religious robes to expensive designer jeans.
Some acknowledged fears of fresh attacks against Hezbollah strongholds.
"Of course, there is a bit of anxiety after the bombings and with all the problems," said Hoda Alameh, a blonde resident of the south Beirut Dahiyeh district, wearing white-framed sunglasses and a black tracksuit.
"But the men here are taking care of security and we have the Lebanese army too, so I think we are safe," she added.
"And there's nothing better than being here. It's my first time participating and... it's such a beautiful experience to have together."
Rabia al-Haj stood by a stall where a man and a woman prepared the Ashura dish of harisseh -- a wheat stew -- in two giant cauldrons.
"This is a religious duty to be here and to remember our Imam Hussein," the 50-year-old said.
"We're not afraid. We don't care what people say or threaten, this is for Imam Hussein."
Hezbollah's role in Syria, where more than 120,000 people have died since the uprising erupted in March 2011, has drawn international criticism.
But some in the crowds, like Dahiyeh resident Zahraa Harb, drew a direct link between Imam Hussein and Hezbollah's fight in Syria.
"Imam Hussein stood up and was martyred for justice, freedom and what is right, and those fighting in Syria are following in his footsteps," she said.