At least seven people were killed on Friday in demonstrations over a film made in the US that mocks Islam - as protests spread around the world.
Three people were killed when the US embassy in Khartoum was attacked, Sudanese state radio said.
In Tunisia, two people were killed after crowds breached the US embassy compound in Tunis. There was one death in Egypt and one in Lebanon.
Protests began on Tuesday against the film, Innocence of Muslims.
The film depicts the Prophet Muhammad as a womaniser and leader of a group of men who enjoy killing. Clips were distributed online with an Arabic voice-over.
The film's exact origin and the motivation behind its production remain a mystery.
In Khartoum, a crowd of several thousand attacked the US embassy. State radio said three people were killed.
The crowds gathered first outside the German embassy, setting it partially alight and causing extensive damage.
The UK embassy nearby was also targeted by protesters but escaped major destruction.
The controversial film has no known links to either Germany or the UK.
Both countries confirmed all their staff in their Khartoum embassies were safe.
"I condemn in the strongest possible terms today's attack and call on the Sudanese authorities to ensure that those involved are brought to justice," said UK Foreign Secretary William Hague.
Later, US Vice President Joe Biden called his Sudanese counterpart Ali Osman Taha to express concern over the security of US and other diplomatic missions in Khartoum, the White House said.
In Tunis, hundreds of protesters entered the embassy compound and set fire to several vehicles in the car park.
Earlier reports said three people had been killed but this was later revised down to two.
Police fired shots, but it was not clear whether these were rubber bullets or live rounds.
Demonstrators raised a black flag bearing the Islamic proclamation of faith: "There is no god but Allah and Muhammad is his messenger."
The American school in Tunis was looted and set on fire.
The leader of Tunisia's moderate Islamist Ennahda movement, Rachid Ghannouchi, said the attacks were unacceptable.
All the dead are believed to be protesters. There is no indication that any diplomatic staff or members of the security forces were killed.
At least one person was killed in Cairo as protests raged for a fourth day.
Police firing tear gas pushed about 500 demonstrators back from the US embassy. Streets nearby were blocked with barbed wire, concrete and police vehicles.
Islamist groups and others had called for a peaceful "million-man march" in the city, but a number withdrew those calls on Friday.
The Muslim Brotherhood, which backs Egyptian President Mohammed Mursi, said it would organise marches and sit-ins in front of mosques - but none outside the US embassy in Cairo.
After talks with Italian leaders in Rome, Mr Mursi reiterated his government's determination to protect foreign diplomats on its soil. He also condemned the film as unacceptable.
Later on Friday, Islamic militants attacked an international observer post in Egypt's restive Sinai region.
The base is not far from the border with Gaza and Israel. It houses some 1,500 members of the multinational force, including US troops.
There were also protests in the northern city of Alexandria.
In other developments:
- In the Yemeni capital Sanaa, security forces fired warning shots and water cannon to disperse protesters near the US embassy
- The US is sending a fast-response team of 50 marines to Sanaa to boost security
- In the Lebanese city of Tripoli, protesters set fire to a KFC fast-food restaurant, sparking clashes with security forces
- In Bangladesh, thousands of demonstrators demanded harsh punishment for the film's makers, and burned the American flag
- In London, about 200 protesters gathered outside the US embassy, burning the US and Israeli flags but there was no violence
- About 1,000 people joined a protest in the eastern Afghan city of Jalalabad, burning an effigy of US President Barack Obama
- Thousands of Palestinians demonstrated in the Gaza Strip and East Jerusalem
- In Nigeria, police in the flashpoint northern city of Jos fired live rounds at a protest outside a mosque
- There were also protests in eastern Sri Lanka and in the Maldives
The protests against the film began on Tuesday in Cairo.
They spread to the Libyan city of Benghazi, where demonstrators stormed the US consulate, killing the ambassador and three other Americans.
President Obama and Secretary of State Hillary Clinton have attended a ceremony at Andrews Air Force Base for the return of the remains of the Americans killed.
Mr Obama said the US would "stand fast" against the violence at its diplomatic missions.
The US has said it is stepping up security at its missions globally in the wake of the attack.
The BBC has been told that the US consulate in Benghazi was not given the standard security contract offered to most US diplomatic missions in the Middle East.
The allegation came from Western private military contractors.
A White House spokesman has said there was no "actionable intelligence" in advance about the Benghazi attack.
President Obama has now ordered a review of security at US diplomatic facilities around the world.