US President Barack Obama rejected any denigration of Islam but said there is no excuse for attacks on US embassies, insisting he will never tolerate efforts to harm Americans.
"I have made it clear that the United States has a profound respect for people of all faiths," Obama said on Saturday during his weekly radio address. "Yet there is never any justification for violence."
Throngs marched through Sanaa, Khartoum, Tunis and other cities after Friday prayers as part of the ongoing wave of demonstrations against the trailer of a film made in the US that is said to insult Prophet Muhammad.
About 500 protesters gathered outside the US consulate on Saturday in the Australian city of Sydney, hurling bottles and shoes.
Police pushed back the crowd, provoking anger among some of the protesters, many of whom had brought their children with them.
The US has sent troops to protect its diplomatic presence in Libya, Yemen and Sudan, where three people died in Khartoum, the capital, during clashes, as the German and British embassies were also attacked.
Al Jazeera's Harriet Martin, reporting from Khartoum, said: "The Sudanese authorities are taking things very seriously as they have deployed many, many riot police in the direction of the US embassy."
Amid the developments, Leon Panetta, US defence secretary, announced late on Friday that the US was positioning military forces so that it could respond to unrest in as many as 17 or 18 places in the Islamic world, .
"We have to be prepared in the event that these demonstrations get out of control," Panetta told Foreign Policy magazine.
Wave of protestsUS Marine Corps troops have already arrived in Yemen's capital Sanaa, where four people were killed near the US embassy on Friday. "Today is your last day, ambassador", and "America is the devil", some placards carried by the protesters said.
In Gaza, thousands of people rallied at demonstrations in Gaza City and the southern town of Rafah, a day after the ruling Hamas urged citizens to turn out for protests after Friday prayers.
Protesters waved the flags of the Hamas and Islamic Jihad movements, and set fire to American flags, chanting "Death, death to America, death, death to Israel".
The film was blamed for an attack on the US consulate in Libya's eastern city of Benghazi that killed the US ambassador and three other Americans on Tuesday, the anniversary of the September 11, 2001, al-Qaeda attacks on the US.
Al Jazeera's Hoda Abdel Hamid, reporting from Benghazi, said: "There is a lot of tension in Benghazi people are confused.
"They want to protest but after what took at the US consulate, people are apprehensive, Libyan authorities still believe it was a planned attack at the embassy."
In Nigeria, where radical Islamist group Boko Haram has killed hundreds this year as part of an armed campaign, troops opened fire in the air outside a mosque to disperse protesters in the city of Jos.
In Tunis, the Tunisian capital, two people were killed in clashes on Friday with the police as crowds scaled the US embassy walls and set fire to trees within the compound. An American school was also set on fire by an angry mob.
Crowds also gathered against in Lebanon, where two people were killed, and for the second day in Malaysia, Bangladesh and Iraq.
In Egypt, the ruling Muslim Brotherhood said it would organise marches and sit-ins in front of mosques, but none outside the US embassy in Cairo.
People protesting against the video also clashed with police near the US embassy in Cairo.
Riot police there eventually managed to clear the area around the US embassy from demonstrators after clashes in Tahrir square.
Al Jazeera's Rawya Rageh, reporting on Friday, said protesters belonging to ultra-conservative groups in Sinai stormed a camp for the UN multinational peacekeepers in Sheikh Zuwayed town.
They brought down the flag and placed a black banner with the words "There's no God but Allah, Muhammad is the Prophet of Allah."
Egypt has said the US government, which has condemned the film, should not be blamed for it, but has also urged the US to take legal action against those insulting religion.
After talks with Italian leaders in Rome, President Mohammed Morsi reiterated his government's determination to protect foreign diplomats on its soil. He also condemned the film as unacceptable.
In Libya, authorities said they had made four arrests in the investigation into the attack that killed Ambassador Christopher Stevens. US officials said it may have been planned in advance - possibly by an al-Qaeda-linked group.
Hillary Clinton, the US secretary of state, has said the US has nothing to do with the crudely made film posted on the internet,which she called "disgusting and reprehensible".
The top US military commander called a Christian pastor in Florida to ask him to withdraw his support for it.
The protests present Obama with a new foreign-policy crisis less than two months before seeking re-election and tests US relations with democratic governments it helped to power across the Arab world.
He has pledged to bring those responsible for the Benghazi attack to justice, and the US sent warships towards Libya which one official said was to give flexibility for any future action.Jay Carney, a White House spokesperson, said the administration was monitoring events in the Muslim world.
"President Obama is following events, the violence is not justifiable, the president is making sure in his conversations with leaders in the region that the safety of US representation is respected in their countries," he said.
Nakoula Bessely Nakoula, the man thought to be behind the anti-Islam video, has been taken in for questioning by police in California to answer to possible probation violations, according to Al Jazeera.
Nakoula was previously convicted of financial crimes.
- Al Jazeera