BEIRUT -- The head of Lebanon's powerful Hezbollah movement appeared Monday at a massive rally assailing the United States and warning that broadcast of a film produced in California mocking Islam could have grave consequences.
"America must understand that releasing the entire film will have dangerous, very dangerous repercussions around the world," an emotional Sheik Hassan Nasrallah, Hezbollah's secretary-general, told supporters gathered in a Beirut suburb.
The appearance suggested that Hezbollah, an influential political and military force in Lebanon, is determined to place itself in the vanguard of global Muslim outrage against the incendiary film.
The gathering was among a string of demonstrations in Muslim communities from Tunis to Jakarta after the release on the Internet of a trailer for the amateur, privately produced film, which ridicules the Prophet Muhammad and the Islamic faith. The day's protests in South Asia turned violent and left at least one person dead.
Tens of thousands of pro-Hezbollah supporters attended the rally in Beirut's Dahiyeh suburb, a stronghold where the group has the ability to stage highly disciplined actions. The gathering was boisterous but peaceful and occurred far away from the heavily fortified U.S. Embassy.
The participation of Nasrallah, who seldom appears in public reportedly for fear of assassination, underscored Hezbollah's apparent determination to use the outrage generated by the film to bolster its standing as a moral force in the Arab world. The group's strong backing of Syrian President Bashar Assad, who is facing a bloody uprising, has cost it considerable support among many Arabs.
On Sunday, a Hezbollah-controlled television station, Al-Manar, reported Nasrallah regarded the issue of the film as "more serious than what's going on in Syria" -- a position disputed by Syrians and others who say Assad's forces have killed thousands of civilians.
During Monday's rally, Nasrallah demanded that the United States and the international community block release of the full film. He insisted the trailer should no longer be available on the Internet and called for a boycott of websites that show the video.
In his comments Sunday, the Hezbollah chief dismissed as "hypocrisy, deception and double standards" the Western arguments that blocking the video would violate freedom of speech. He called for "an international resolution criminalizing the defamation of heavenly religions."
The U.S. classifies Hezbollah as a terrorist organization.
While the Hezbollah gathering was peaceful, protesters infuriated by the film clashed with police Monday in the capital of Afghanistan, setting cars and tires ablaze and chanting anti-American slogans.
Police blocked off the traffic circle closest to the U.S. Embassy and other diplomatic missions in Kabul, and most Westerners working in the capital were ordered by their organizations to try to stay out of public view.
Monday's unrest broke out when about 1,000 people gathered near an American base on the eastern edge of the capital and began marching toward the center of the city. Police fired shots into the air to try to disperse the crowd, but the protesters continued to surge forward.
President Barack Obama phoned Afghan President Hamid Karzai, urging him to do what he could to stave off violence. Karzai did not personally issue a public call for calm, but aides said he warned local officials and religious leaders against inciting riots.
In neighboring Pakistan, protests against the film intensified Monday as demonstrators set ablaze buildings in the northwest and hurled stones at riot police in the southern city of Karachi, the nation's commercial hub.
At least one protester was killed when about 800 demonstrators clashed with police in the northwest region of Upper Dir, along the Afghan border, authorities said. Protesters torched a press club and the homes and offices of government officials, said Muhammad Mukhtiar, a police officer. Five people were arrested.
Police did not say how the demonstrator was killed.
In Karachi, hundreds of students affiliated with a fundamentalist organization, Islami Jamiat-e-Talaba, set American flags on fire, burned tires in the street and threw stones at police, authorities said. Police fired tear gas at demonstrators and arrested at least 40 people.
With the protests ratcheting up, Pakistani Prime Minister Raja Pervez Ashraf ordered the blocking of YouTube, the website on which a video trailer of the film has been posted. According to a statement issued by Ashraf's office, he issued the order after YouTube "refused to heed the advice of the government of Pakistan to remove the blasphemous film from its site."