* Hezbollah chief calls for rally in Beirut
* Nationwide protests planned for later this week
By Oliver Holmes
BEIRUT, Sept 17 (Reuters) - Supporters of the Shi'ite militant group Hezbollah are set to hit the streets of Beirut on Monday after its leader Sayyed Hassan Nasrallah called for protests against a film that portrays the Prophet Mohammad as a womaniser and a fool.
Lebanon has already seen protests over the Internet video in the mainly Sunni Muslim city of Tripoli. One person was killed and 14 wounded in clashes with security forces on Friday after Islamist protesters set fire to a U.S. fast food restaurant.
Nasrallah, who heads the largest armed force in Lebanon, has the ability to muster huge numbers of Shi'ite Muslims in the Mediterranean state of 4 million people.
Days of anti-American violence provoked by the amateurish video, produced in California, have put Western embassies across the Muslim world on high alert. Protests have erupted from London to Lahore.
"We call for protests tomorrow in the southern suburbs (of Beirut) at 5 o'clock (1400 GMT)," Nasrallah said in a televised speech late on Sunday evening.
"Muslims and Christians must remain vigilant in order to refrain from sliding towards strife. Those responsible for the film, starting with the U.S., must be held accountable."
"All these developments are being orchestrated by U.S. intelligence," he said. He accused Washington, which denies any involvement with the film, of using the pretext of freedom of speech to justify the continued availability of the film online.
Nasrallah, a powerful figure who has the backing of Shi'ite Iran, also called for demonstrations in other parts of Lebanon, including the southern coastal town of Tyre on Wednesday and the northern town of Hermel on Sunday.
Nasrallah urged the Lebanese government to act decisively.
Shortly afterwards, Lebanese Foreign Minister Adnan Mansour told Reuters he had called Arab League Secretary-General Nabil El-Araby to ask him to organise an emergency meeting of Arab foreign ministers to discuss the film.
Lebanon holds the rotating presidency of the Arab League's Foreign Ministers' Council.
The video, circulating on the Internet under several titles including "Innocence of Muslims", shows the Prophet in a sexual act with a woman.
Many Muslims consider any depiction of the Prophet offensive.
The U.S. ambassador to Libya, Christopher Stevens, and three other Americans were killed in Benghazi, Libya, last Tuesday in an attack on the U.S. consulate that coincided with an upsurge of anger about the film.
At least nine people were killed in protests in several countries on Friday, yet protests largely subsided over the weekend.
After Stevens' death, Hezbollah sent out a statement condemning the film as an "immoral act ... of the highest degree" on Wednesday, but did not call for protests.
Pope Benedict left Lebanon on Sunday after a three-day visit, supported by Nasrallah, in which he urged Arab leaders to serve justice and peace.