US diplomatic missions are on high alert around the world as protests and demonstrations against the anti-Islam video directed by controversial filmmaker Nakoula Basseley Nakoula, have snowballed across northern Africa and the Middle East.

As protesters rallied in front of US embassies and Western diplomatic posts in 10 nations, a US intelligence bulletin has warned that the wave of anger, which has already cost the lives of the US ambassador to Libya, Chris Stevens, and three embassy staff, as well as protesters in Yemen and Lebanon, could worsen.

"The risk of violence could increase both at home and abroad as the film continues to gain attention," the bulltein warned.

"First responders should remain aware of the potential for spontaneous large crowds and protests that could overwhelm resources and should be vigilant for possible efforts to encourage peaceful protesters to commit acts of violence."

Concerns are especially as Friday prayers often give fresh impetus to protests.

Protests started in Egypt after the trailer for Innocence of Muslims, a film reportedly shot in California by an anti-Islam extremist who had a past jail sentence for cooking methamphetamine, was dubbed in Arabic and posted online.

In Cairo, protesters climbed over the walls of the US embassy and hauled down the American flag, replacing it with an Islamic banner. Demonstrations and clashes with the police were still going on.

As protests rippled across the region, demonstrators took to the streets of Benghazi in Libya and stormed the US diplomatic mission. Four embassy staff including the ambassador to Libya were killed.

From there, the anger quickly spread to other countries.

Five thousand protesters tried to invader the US embassy in Sana'a, the capital of Yemen. Security guards opened fire and four protesters died during clashes, Yemeni security officials said.

People angry at the movie, which mocks the Prophet Mohammed, gathered in front of US embassies in Morocco and Tunisia. Palestinians rallied outside UN headquarters in Gaza City, while a small group of people demonstrated in front of the of the US embassy in Tel Aviv.

Demonstrators chanted anti-US songs and burned American flags in Baghdad, Iraq, and in front of the Swiss embassy in Tehran. The Swiss diplomatic mission represents US interests in the state as Washington and Tehran cut direct diplomatic relations.

Scuffles between protesters and police have also been reported in the Indian province of Kashmir, Sudan and Bangladesh.

Both violent protests and the movie were severely condemned by head of states all around the world.

"Nothing justifies such killings and attacks," said UN secretary-general Ban Ki-moon.

"The hateful film appears to have been deliberately designed to sow bigotry and bloodshed."

Libya's prime minister said protests were wrong to target the US government over the film.

"The people, they don't understand that such a case like this, the American government has nothing to do with it. Somebody made a film and they put it on YouTube. It was very offensive for sure but that doesn't justify taking this wild actions against Americans or American embassies. People can come out and demonstrate and express their opinion peacefully," Mustafa Abu Shaqur told the BBC.

US president Barack Obama strongly condemned the "outrageous" attacks and said that the US was to work with the Libyan government to apprehend the killers.

Libyan authorities have arrested four people in connection with the attack on the US consulate in Benghazi.