BEIRUT - The head of Lebanon's Shi'ite terrorist group Hezbollah on Sunday called for nationwide protests against a film mocking the Prophet Mohammad, saying the United States must be held accountable for the Internet video. Western embassies across the Muslim world remained on high alert and the United States urged vigilance after days of anti-American violence.

"We call for protests tomorrow in the southern suburbs (of Beirut) at 5 o'clock," Hezbollah Secretary-General Hassan Nasrallah said in a televised speech.

"Muslims and Christians must remain vigilant in order to refrain from sliding towards strife. Those responsible for the film, starting with the US, must be held accountable.

"All these developments are being orchestrated by US intelligence," he said, adding that the US government was using the excuse of freedom of speech in order to justify the continued broadcast of the film.

Nasrallah also called for demonstrations around Lebanon, including the southern coastal town of Tyre on Wednesday and the northern town of Hermel on Sunday.

The video, circulating on the Internet under several titles including "Innocence of Muslims", portrays Mohammad as a womanizer and a fool. In one clip posted on YouTube, Mohammad was shown in a sexual act with a woman.

Many Muslims consider any depiction of the prophet as offensive and fury about the film tore across the Middle East this week, with protesters attacking US embassies and burning American flags.

The US ambassador to Libya, Christopher Stevens, and three other Americans were killed in Benghazi, Libya, last Tuesday. At least nine people were killed in protests in several countries on Friday, but protests subsided over the weekend.

Nasrallah's speech came a few hours after Pope Benedict left Lebanon for the Vatican, ending a three-day tour in which he urged Arab leaders to serve justice and peace.

Nasrallah, head of the strongest armed force in the country, said in a statement last week that he supported the visit.

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