Libya said last night it had arrested several suspects over the attack on the US consulate in Benghazi that killed ambassador Chris Stevens and three other US nationals.
The country's Deputy Interior Minister, Wanis al-Sharef, declined to give any details of the number of people in custody or their backgrounds "so as not to hamper the smooth running of the investigation".
"The Interior and Justice ministries have begun their investigations and evidence-gathering and some people have been arrested," Mr Sharef said late last night.
Egypt's ruling Muslim Brotherhood has called for nationwide protests today against the US-produced low-budget movie deemed offensive to Islam which triggered the attacks.
The Obama administration responded to the death of Mr Stevens, 52, by sending two navy destroyers and elite marines to the coast of North Africa yesterday.
Federal investigators and an intelligence team were in Libya amid suspicions the violence in eastern Benghazi - on the anniversary of the September 11, 2001, attacks - was planned by extremists.
As the US struggled to piece together events around the deaths, clashes continued last night near the US embassy in Cairo. In the Yemeni capital, Sanaa, hundreds of protesters chanting "death to America" stormed the US embassy compound, burning the American flag.
Protesters smashed windows as they breached the embassy perimeter, before being driven off by Yemeni security forces, who killed one protester and wounded five.
Protests against the anti-Islam film, Innocence of Muslims, were also held in Gaza, Morocco, Sudan, Tunisia, Iran and Iraq.
International condemnation continued over the killings. All US diplomatic staff from Benghazi were evacuated to the Libyan capital, Tripoli.
President Barack Obama ordered the upgrading of security at US diplomatic missions around the world. "Make no mistake, we will work with the Libyan government to bring to justice the killers who attacked our people," he said.
He telephoned the leaders of Egypt and Libya last night to urge them to work with US agencies to protect US personnel. Mr Obama told Egyptian President Mohammed Morsi that while he "rejects efforts to denigrate Islam, there is never any justification for violence against innocents".
Mr Morsi, speaking in Brussels, last night vowed to protect foreign embassies in Cairo. Mr Stevens was a popular career diplomat. During the uprising against Libyan dictator Muammar Gaddafi, he was Washington's contact with the rebels. After the fall of Gaddafi, he was hand-picked by Mr Obama to be US ambassador.
While US officials cautioned that investigators had yet to clarify the events that led to the killings, they believed Mr Stevens became separated from his security officer as flames engulfed the building.
The Wall Street Journal reported that locals pulled Mr Stevens from the burning and smoke-filled building about 1am. He was driven to Benghazi Central Hospital, where the staff tried in vain to revive him.It is believed that Mr Stevens died of smoke inhalation.
In Benghazi yesterday hundreds of Libyans protested against the killing of the Americans, blaming Islamic extremists.
Thousands of protesters in Cairo are expected to take up the call by the Muslim Brotherhood to protest against the US film tonight after Friday prayers.
Many say the protests in several Islamic countries were sparked by Innocence of Muslims, a low-budget film made by a man in California using the name Sam Becile.
Doubts emerged yesterday whether any such person exists, with suggestions the name is one of many pseudonyms used by a Coptic Christian who has been convicted over financial crimes.
The trailer for the film, posted recently on YouTube after being dubbed in Arabic, describes the Prophet Mohammed as "a murderous thug" and suggests he was a child molester.
President Hamid Karzai cut access to YouTube to prevent Afghans seeing the extracts. Cancelling a visit to Norway, he said the film had "stoked interfaith enmity and confrontation", but he did not express regret for the US deaths.
