Hezbollah warned of "very dangerous" global repercussions if an anti-Islam film is released in its entirety, as a fatwa was issued against the film's producer who has gone into hiding with his family.
Hezbollah's Hassan Nasrallah warning came Monday as the death toll from a week of violence sparked by the movie rose to 19.
An eruption of Muslim anger over a trailer of the American-made film that appeared on the Internet has spread across the world, taking hold Monday in Afghanistan, Indonesia, the West Bank, the Philippines and Yemen.
Tens of thousands of demonstrators poured into the streets of southern Beirut to denounce the film at Nasrallah's request, and the head of the powerful Shiite Muslim group surprised supporters by making a rare public appearance.
Nasrallah, whose Lebanese movement is blacklisted in the United States as a terrorist group, has called for a week of protests across the country over the film, describing it as the "worst attack ever on Islam".
"America must understand... the US must understand that releasing the entire film will have dangerous, very dangerous, repercussions around the world," he told the rally.
The filmmaker Nakoula Basseley Nakoula, a 55-year-old Egyptian Copt and fraudster who was sentenced to 21 months in prison in the US in June 2010, has not been seen since Saturday when he was questioned by his US parole officer.
The risks now facing those involved in the production of the film "Innocence of Muslims", which depicts the Prophet Mohammed as a thuggish womaniser, were underlined when a Salafist cleric in Egypt called Monday for the deaths of all those involved in its making.
The film producer's family joined him in hiding, as more cast members of the film that outraged the Islamic world insisted they had been duped into making it.
The terrorism monitoring service SITE Intelligence Group said Ahmad Fouad Ashoush issued his fatwa, or religious edict, against the cast and crew of "Innocence of Muslims" via jihadist Internet forums over the weekend.
"I issue a fatwa and call on the Muslim youth in America and Europe to do this duty, which is to kill the director, the producer and the actors and everyone who helped and promoted the film," the cleric said.
The controversial movie has sparked a week of furious protests outside US embassies and other American symbols in at least 20 countries.
In Pakistan, thousands of students burned US flags and chanted anti-American slogans in the northwestern city of Peshawar, where Osama bin Laden kept a home during the 1980s jihad against Soviet troops in adjacent Afghanistan.
In the nearby district of Upper Dir, a protester was killed and two others wounded in a shootout with police.
In Karachi, Pakistan's biggest city, another demonstrator died after being shot in the head during clashes with police near the US consulate on Sunday.
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The US embassy in Islamabad was closed on Monday because of the risk of demonstrations and diplomats have been banned from all but essential travel throughout the country.
In neighbouring Afghanistan, protests turned violent for the first time when more than 1,000 people rallied in Kabul, setting police cars and containers ablaze, police told AFP.
Between 40 and 50 policemen were "very slightly wounded" by stone-throwers and members of the crowd waving sticks, said Kabul police chief Mohammad Ayoub Salangi.
Google has barred access to the video of the film in Egypt, India, Indonesia, Libya and Malaysia, while the government has restricted access to Google-owned YouTube in Afghanistan.
Later, Pakistan blocked access to YouTube after an order from Prime Minister Raja Pervez Ashraf to do so, following the video-sharing website's failure to take down the anti-Islam film.
Attempts to access YouTube met with a message saying the website had been classed as containing "indecent material".
In Jakarta, protesters hurled petrol bombs and clashed with Indonesian police outside the US embassy shouting "America, America go to hell", as demonstrations in the world's most populous Muslim nation turned violent.
The capital's police chief Untung Rajab said 11 policemen and a protester were injured and taken to hospital, and that four protesters were arrested.
Mass demonstrations after the main weekly Muslim prayers on Friday saw 11 protesters killed as police battled to defend US missions from mobs in Egypt, Lebanon, Sudan, Tunisia and Yemen.
The unrest began in Cairo, where protesters stormed the US embassy late Tuesday, replacing the Stars and Strips with an Islamic flag.
Hours later it spread to the eastern Libyan city of Benghazi, where the US consulate came under sustained attack, killing four Americans, including ambassador Chris Stevens.
In Afghanistan, two US Marines died and six US fighter jets were destroyed when Taliban fighters on Friday stormed a giant airfield to avenge the film.
The United States has deployed counter-terror Marine units to Libya to protect its embassy in Tripoli and stationed two destroyers off the North African coast.
A Marine unit was also dispatched to protect the US embassy in Yemen, where police shot dead four protesters and wounded 34 others on Thursday as a mob breached its perimeter. There were more protests in Yemen on Monday.
The United States has evacuated all non-essential staff and family members from Sudan and Tunisia and warned US citizens against travel to the two countries.
Libya said it has arrested 50 suspects in connection with the consulate attack.