Violence erupted in downtown Beirut on Sunday as protesters tried to storm the offices of Prime Minister Najib Mikati after the funeral of an assassinated intelligence chief whose death they blame on Syria.
Security forces shot into the air and police fired tear gas to repulse the hundreds of protesters who overturned barriers and threw stones and steel rods, witnesses said.
The clashes fed into a growing political crisis in Lebanon linked to the civil war in neighboring Syria.
An angry crowd had marched on the prime minister's office after politicians at the funeral of Brigadier General Wissam al-Hassan, who was killed by a car bomb on Friday, called on Mikati to resign over the killing.
The opposition and its supporters believe Mikati is too close to Syrian President Bashar Assad and his Lebanese ally Hezbollah, which is part of Mikati's government.
Many of the protesters waved flags from the anti-Syrian opposition Future Movement - a mainly Sunni Muslim party - and Christian Lebanese Forces as well as black Islamist flags.
They scattered after the security forces' action and there were no immediate reports of any casualties other than two people fainting.
Opposition leader Saad Hariri urged supporters to refrain from any more violence.
"We want peace, the government should fall but we want that in a peaceful way. I call on all those who are in the streets to pull back," Hariri told supporters after the attack, speaking on Future Television channel.
Senior intelligence official laid to rest
Hassan, 47, was a Sunni Muslim and senior intelligence official who had helped uncover a bomb plot that led to the arrest and indictment in August of a pro-Damascus former Lebanese minister.
He also led an investigation that implicated Syria and the Shi'ite Hezbollah in the assassination of Lebanon's former prime minister Rafik Hariri in 2005.
Thousands of people had filled central Martyrs' Square for his funeral ceremony, accusing Syria of involvement in the killing and calling for Mikati to quit.
One banner read "Go, go Najib" echoing the slogans of the Arab Spring.
The violence broke out after Fouad Siniora, a former prime minister, said in a speech that the opposition rejected any dialogue to overcome the political crisis caused by the assassination unless the government first resigned.
"No talks before the government leaves, no dialogue over the blood of our martyrs," Siniora said to roars of approval from the crowd.
At the start of the funeral, senior politicians and the military and security top brass turned out at the Internal Security Force headquarters for a ceremony held with full military honors and broadcast live on national television.
Hassan's wife and two sons, the youngest weeping, listened as he was eulogized by the head of police, Ashraf Rifi, and President Michel Suleiman.
Suleiman said the government and people must work "shoulder to shoulder" to overcome the challenges posed by the killing.
"I tell the judiciary do not hesitate, the people are with you, and I tell the security be firm, the people are with you, with you. And I tell the politicians and the government do not provide cover to the perpetrator."
In keeping with custom for state funerals, church bells pealed as police officers carried the flag-draped coffins of Hassan and his bodyguard to the mosque on Martyr's Square through chanting crowds. Muslim prayers were broadcast by loudspeaker from the mosque.
In the build-up to the funeral, people at the square had said they saw Syria's hand in the bombing.
"We blame Bashar Assad, the president of Syria," said Assmaa Diab, 14, from the northern Lebanese city of Tripoli, Hassan's home town. She was in the square with her sister and father.
"He is responsible for everything - in the past, now, and if we don't stand up to him, the future," she said.
The prime minister was also a focus of their anger.
"We are here to tell Mikati we don't need him any more and to tell Hezbollah we don't want any more of their games," said Hamza Akhrass, a 22-year-old student who from south Lebanon.
"Mikati takes too much pressure for Syria."
One banner read: "People want the overthrow of Najib."
Mikati said on Saturday he had offered to resign to make way for a government of national unity but he had accepted a request by President Michel Suleiman to stay in office to allow time for talks on a way out of the political crisis.
Sunday's events highlighted how the 19-month-old uprising against Assad in Syria has exacerbated deep-seated sectarian tensions in Lebanon, which is still scarred from its 1975-90 civil war.
Sunni-led rebels are fighting to overthrow Assad, who is from the Alawite minority, which has its roots in Shi'ite Islam. Lebanon's religious communities are divided between those that support Assad and those that back the rebels.
Mikati sought in vain to insulate the country from turmoil in its larger neighbor, which has long played a role in Lebanese politics. He himself said he suspected Hassan's assassination was linked to his role in uncovering Syrian involvement in the August bomb plot.