Protests against an anti-Islam film made in the US have spread across the Middle East and North Africa.
In Yemen, demonstrators briefly stormed the grounds of the US embassy in Sanaa and burnt the US flag, but were driven back by security forces.
In Egypt, 224 people were injured in protests, the health ministry said.
In Libya, where the US ambassador was killed during protests in Benghazi on Tuesday, officials said they had made some arrests over the attack.
US officials say they are investigating whether the attack in Libya was planned, citing suspicions that a militant jihadist group may have co-ordinated the violence.
Libya's new Prime Minister Mustafa Abu Shagur told the AFP news agency there had been a "big advance" in the investigation in Benghazi.
"Arrests have been made and more are under way as we speak," he said.
Deputy Interior Minister Wanis al-Sharif said that police were gathering evidence and, in addition to those arrested, some militants were being closely monitored.
US Secretary of State Hillary Clinton condemned the film which gave rise to the protests as "disgusting" and "reprehensible".
The US utterly rejected its contents and its message, she said, but the film was no excuse for violence.
Police in Sanaa shot in the air, but failed to prevent crowds from gaining access to the embassy compound and setting fire to vehicles.
Security force reinforcements used tear gas, water cannon and live fire to drive protesters back.
There were reports of injuries on both sides, although the Reuters news agency carried a statement from the embassy saying there were none.
Windows were smashed. A US flag was torn down and replaced with a black flag bearing the Muslim statement of faith, "There is no god but Allah".
In Washington, a White House spokesman said all those working in the Sanaa embassy were safe and accounted for.
In Egypt, protests erupted for a third day outside the US embassy in Cairo, with some demonstrators demanding the expulsion of the ambassador.
Police fired tear gas at crowds throwing stones.
Islamist groups and others have called for a "million-man march" in Cairo on Friday.
The Muslim Brotherhood, the Salafist al-Nour party and non-religious groups including the "Ultra" fans of Zamalek football club have invited Muslims, Coptic Christians and all Egyptian citizens to join them.
President Mohammed Mursi appealed for calm, saying Egyptians "reject any kind of assault or insult" against the Prophet Muhammad.
"I condemn and oppose all who... insult our prophet. [But] it is our duty to protect our guests and visitors from abroad," he said in a statement broadcast by state media.
"I call on everyone to take that into consideration, to not violate Egyptian law... to not assault embassies."
In other developments:
- Mr Abu Shagur says there is "no justification" for the Benghazi attack and investigations are under way to find the "criminals" responsible
- Russia says it fears "chaos" in the Middle East and Saudi Arabia condemns both the film and the violence
- Iranians chanting anti-US and anti-Israel slogans stage a protest outside the Swiss embassy in the Iranian capital, Tehran, which represents US interests
- Afghan President Hamid Karzai has postponed a planned visit to Norway, fearing violence could erupt in his country
- There were small protests in Bangladesh and Iraq, in addition to Morocco, Sudan and Tunisia
- Security has been increased at US embassies and consulates around the world; US officials say a marine anti-terrorism team is being deployed to Libya and two destroyers to the Libyan coast as a precautionary measure
'Duty to protect'
US officials have described the Benghazi attack as complex and professional, and suggested the attackers may have used the film protest as a pretext for the attack.
Reuters quoted officials as saying there were suspicions that a militia known as the Ansar al-Sharia brigade was responsible, although the group has denied the claim.
The officials said there were also reports that al-Qaeda's North Africa-based affiliate, al-Qaeda in the Islamic Maghreb, may have been involved, the news agency reports.
The obscure film which has sparked anger, called Innocence of Muslims, was shot in the US and posted online earlier this year. Clips have since been shown on Arab TV stations.
It depicts the Prophet Muhammad as a womaniser and the bloodthirsty leader of a ragtag group of men who enjoy killing.
The BBC's Alastair Leithead says the exact origin of the movie and the internet clip, and the motivation behind its production, remains a mystery.
The most offensive comments regarding Muhammad appear to have been dubbed on later, says our correspondent.
Some of the actors involved have since condemned the film, and said they had no idea it was to be used as anti-Islam propaganda.