Gunmen armed with rifles and rocket-propelled grenades have exchanged fire in southern districts of Lebanon's capital Beirut, security sources said, and residents could also hear the sound of ambulance sirens.
There were no immediate reports of casualties from the clashes on Sunday night, which occurred after angry mourners tried to storm government offices in the centre of Beirut at the end of the funeral of an intelligence official assassinated on Friday.
Violence erupted after protesters tried to storm the offices of Najib Mikati, the prime minister, following the funeral of Wissam al-Hassan, whose death they blame on Syria.
Security forces shot into the air and police fired tear gas on Sunday to repulse the hundreds of protesters who overturned barriers and threw stones and steel rods, witnesses said.
The funeral of Hassan had been billed as a protest against Syrian meddling in Lebanon, but quickly turned into equal, if not greater, anger at Mikati and his government.
An angry crowd had marched on the government's headquarters, or the Serail, after politicians at the funeral called on him to resign over the killing.
Al Jazeera's Gregg Carlstrom, reporting from the scene of the violence, said about 50 opposition supporters tried for up to half an hour to approach the Serail, throwing sticks, rocks and rods until they were dispersed by Internal Security Force (ISF) personnel.
"The whole country will be shut down until Mikati resigns. We are going to block roads, we are going to protest," Ahmad Balaa, a young activist of the opposition March 14 alliance who was among the protesters, told Al Jazeera.
Authorities responded with tear gas and several officers fired machine guns and rifles in the air.
One plainclothes guard pulled a pistol from his belt and fired over protesters' heads. Then a roar of automatic gunfire erupted, sending the protesters scattering for cover. It was unclear if the guards fired live bullets or blanks, but no protesters were reported injured by gunfire.
Several were overcome by tear gas, and the government's media office said 15 guards were injured.
Unrest also broke out elsewhere in Lebanon. Protesters blocked major roads in Beirut and in the north with rows of burning tyres, and briefly closed the country's main highway to the south, the national news agency said.
|Al Jazeera's Hoda Abdel-Hamid reports on
the flare-up of violence in Tripoli
Clashes erupted in the northern city of Tripoli, with residents of two neighbourhoods that support opposite sides in Syria's civil war exchanging gunfire. One woman was killed in the violence.
The latest clashes fed into a growing political crisis in Lebanon linked to the conflict in neighbouring Syria.
The opposition and its supporters believe Mikati is too close to Syrian President Bashar al-Assad and his Lebanese ally Hezbollah, which is part of Mikati's government.
Many of the protesters waved flags from the opposition Future movement - a mainly Sunni Muslim party - and the Christian Lebanese Forces as well as black Islamist flags.
They scattered after the ISF intervention and there were no immediate reports of any casualties other than two people fainting.
Saad al-Hariri, leader of the March 14 opposition alliance, 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, speaking on Future Television channel, told supporters.
Hassan, 47, a Sunni Muslim, had helped uncover a bomb plot that led to the arrest and indictment in August of a pro-Assad former Lebanese minister.
He also led an investigation that implicated Syria and Hezbollah, the powerful, predominantly Shia Muslim-backed group, in the assassination of Rafik al-Hariri, a former prime minister, in 2005.
Speaking at the funeral, President Michel 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," he said.
"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 Martyrs' Square through chanting crowds.
Muslim prayers were broadcast by loudspeaker from the mosque.