• US pledges to aid Beirut bomb probe amid Lebanon violence

    Hussam Shebaro / Reuters

    A Sunni Muslim gunman with a weapon rides a motorcycle through the streets of Kaskas in Beirut, Monday, after a night of tension.

    By NBC News staff and wire reports

    U.S. Secretary of State Hillary Clinton has pledged to help Lebanon investigate Friday's deadly car bombing in Beirut, as parts of the city were engulfed in violence that some observers say heralds the spread of civil war from neighboring Syria. 

    She spoke with Lebanese Prime Minister Najib Mikati on Sunday to reiterate U.S. condemnation of the attack - which killed intelligence chief Brig. Gen. Wissam al-Hassan - calling it "heinous", State Department spokesperson Victoria Nuland said.

    "The secretary emphasized the United States' firm commitment to Lebanon's stability, independence, sovereignty and security," Nuland said in a statement.

    PhotoBlog: Tension on Beirut streets as political crisis deepens

    "She noted the importance of political leaders working together at this sensitive time to ensure that calm prevails and that those responsible for the attack are brought to justice,” the statement said.

    Protesters rushed the prime minister's office Sunday in Lebanon, ripping up barbed wire and hurling rocks. The situation, which started as a peaceful protest, has become a standoff between protesters and the military. It has also triggered concern that Syria's civil war is spreading. NBC's Stephanie Gosk reports.

    Nuland said Clinton and Mikati agreed that the United States "would provide assistance in the investigation of the bombing."

    Syria blamed by Lebanese opposition
    Opposition leaders and their supporters accuse Syria of being behind Friday's attack, and say Mikati is too close to Syrian President Bashar al-Assad and his Lebanese ally Hezbollah, which is part of Mikati's government.

    Thousands turned out Sunday in downtown Beirut's Martyrs' Square for Hassan's funeral, which also served as a political rally. Violence erupted after an opposition leader demanded that Mikati step down to pave the way for talks on the crisis.

    "The Syrian regime started a war against us and we will fight this battle until the end," said Anthony Labaki, a 24-year-old physiotherapist.

    Slideshow: Bombing in Beirut

    Mahmoud Zayyat / AFP - Getty Images

    Huge blast explodes in a central Beirut street injures dozens, kills at least eight.

    Launch slideshow


    Sunday's clashes fed into a growing political crisis in Lebanon linked to the conflict in neighboring Syria. Israeli news site Haaretz reported that the clashes "raised the specter of the nation once again becoming torn apart by civil war."

    A group marched to the prime minister's office, then overturned barriers, pulled apart barbed wire coils and threw steel rods, stones and bottle at soldiers and police.

    Security forces responded by shooting into air and firing teargas, forcing the protesters to scatter.

    "Lebanon is in the eye of the storm," said Fawaz A. Gerges, head of the Middle East Center at the London School of Economics. "The fact that the protesters came close to storming the parliament shows how deep the crisis of the state is and how weak the leadership has become."

    Fire exchanged in southern Beirut
    On Sunday night, gunmen armed with rifles and rocket-propelled grenades exchanged fire in southern districts of Beirut, security sources told Reuters, and residents could hear the sound of ambulance sirens.

    There were no immediate reports of casualties from the clashes in the capital, but in the northern city of Tripoli a 9-year-old girl was killed by a sniper and several people were wounded in clashes.

    PhotoBlog: Violence erupts in Beirut after slain official's funeral

    Gunmen have been patrolling the streets in Tripoli, scene of previous clashes between Sunnis and Alawites sympathetic to different sides in the Syria war.

    Opposition leader Saad al-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 said on the Future Television channel.

    Sectarian tensions
    Sunday's events highlighted how the 19-month-old uprising against Assad has sharpened 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 Shiite Islam. Lebanon's religious communities are divided between those that support Assad and those that back the rebels.

    Hassan, 47, was a senior intelligence official who had helped uncover a bomb plot that led to the arrest and indictment in August of a pro-Assad former Lebanese minister.

    A Sunni Muslim, he also led an investigation that implicated Syria and the Shiite Hezbollah in the 2005 assassination of Rafik al-Hariri, a former prime minister of Lebanon.

    Damascus and Hezbollah have condemned Hassan's killing.

    NBC's Paul Nassar describes the scene after a bomb killed 8 people in Lebanon Friday.

    But mourners at Martyrs' Square on Sunday accused Syria of involvement and called for Mikati to quit. One banner read "Go, go Najib" echoing the slogans of the Arab Spring.

    "We came for Lebanon's future," said mourner Rama Fakhouri, an interior designer. "And to show that we will not be scared."

    Reuters and The Associated Press contributed to this report.

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