GWEN IFILL: Next: Hezbollah and the shifting political landscape in Lebanon.
Margaret Warner has the story.
MARGARET WARNER: Lebanon's president appointed Hezbollah-backed candidate Najib Mikati to be prime minister today, asking him to form a new government. Mikati, a billionaire businessman, also won a majority of Parliament votes, defeating the Western-backed caretaker Prime Minister Saad Hariri.
Demonstrations erupted on the streets, with angry Sunnis protesting Hezbollah's rising power.
WOMAN (through translator): We do not want a prime minister imposed on us. We don't want a prime minister named by Hezbollah. We want Saad Hariri.
MARGARET WARNER: Today, Hariri, who has refused to join the new government, asked his supporters to remain calm.
SAAD HARIRI, acting Lebanese prime minister (through translator): I would like to announce my total rejection of all the riots that accompanied the protests and distorted the national and noble aims for these movements.
MARGARET WARNER: Mikati did the same.
NAJIB MIKATI, candidate for Lebanese prime minister (through translator): I call on the people of Tripoli to restrain themselves and not get drawn into conflict with anyone. Last night, I told you all I have extended my hand to everyone and we are communicating with everyone.
MARGARET WARNER: Mikati's ascendancy is a giant step for Hezbollah, a Shiite-dominated group backed by Iran and Syria and considered a terrorist organization by the U.S.
Mikati, however, is a Sunni. Hezbollah, which began as a resistance group fighting Israeli occupation in Southern Lebanon in the '80s, was blamed for the 1983 bombing of U.S. Marine barracks in Beirut.
More recently, Hezbollah and Israel waged a five-week conflict in 2006. Then, as now, the movement was led by Hassan Nasrallah, who addressed a rally of supporters today.
HASSAN NASRALLAH, Hezbollah leader (through translator): Today, the Lebanese have a good chance to unite under the condition of no winner, no loser. Let us cooperate.
MARGARET WARNER: Today's events were triggered two weeks ago, when Hezbollah pulled out of Hariri's government, bringing it down. Hariri had refused the group's demand to stop cooperating with a United Nations-backed tribunal investigating the 2005 assassination of his father, former Prime Minister Rafik Hariri.
Hezbollah denies any role in the killing, but sealed draft indictments issued last week are reported to name some Hezbollah members.
In Washington, Secretary of State Hillary Clinton expressed misgivings at the prospect of a Hezbollah-led government.
U.S. SECRETARY OF STATE HILLARY RODHAM CLINTON: A Hezbollah-controlled government would clearly have an impact on our bilateral relationship with Lebanon. Our bottom lines remain as they always have been.
First, we believe that justice must be pursued and impunity for murder ended. We believe in Lebanon's sovereignty and an end to outside interference. So, as we see what this new government does, we will judge it accordingly.
MARGARET WARNER: The United States has given $1.2 billion in economic and military aid to Lebanon in the last five years. And the Obama administration had requested $246 million more this year.