The president vowed that “justice will be done” after Mr Stevens, 52, was killed by an Islamist mob in an attack on the US consulate in the eastern coastal city of Benghazi. Three other Americans were also killed in the raid, which came on the anniversary of September 11.
The attack was initially thought to have been the work of a spontaneous mob, provoked by a US-made film ridiculing the Prophet Mohammed that had been highlighted by media outlets across the Middle East.
However, there was mounting speculation that the attack on the Benghazi consulate, which also killed a second diplomat, Sean Smith, and two other US officials, had been carefully planned by al Qaeda linked Islamic extremists.
The attackers were apparently armed with mortars and rocket propelled grenades, while there was speculation of links with the death of al Qaeda’s deputy leader or the 11th anniversary of the terrorist attacks on New York and Washington.
Speaking in the Rose Garden outside the White House yesterday, Mr Obama confirmed that a 50-strong US Marine anti-terrorist security team had been dispatched to Libya to bolster security and aid efforts to find those responsible.
“Make no mistake. Justice will be done,” he said. “The United States condemns in the strongest terms this outrageous and shocking attack,”
He paid tribute to the work of Mr Stevens, who had led American diplomatic efforts to liberate Benghazhi last year, saying that he died in a city “he helped save”. The attacks were also swiftly condemned as “cowardly” by Libya’s interim government and by the international community.
“We extend our apology to America, the American people and the whole world,” said Libya’s interim president, Mohammed el-Megarif.
Although precise details of the attack were still unclear last night, claims that it could have been a deliberate, targeted assault gathered strength.
A senior US official told the CNN network that a grenade had set a building inside the walled consulate compound ablaze, leaving the Americans facing both a fire inside and attackers outside.
Mr Stevens and the others who died were separated from the rest of the staff while trying to escape to the roof of the building and succumbed to smoke inhalation, the senior official said. Mr Stevens is the first US ambassador to be killed in the line of duty since 1979.
Doctors at the Benghazi Medical Center said Mr Stevens had been at the point of death when he was brought into the facility by several friendly Libyans. “We tried to revive him for an hour and a half but with no success,” Dr Ziad Abu Zeid said.
The Quilliam Foundation, an anti- extremist think-tank in London, speculated in a statement that the attacks could have been linked by a promise this week by the Al Qa’eda leader Ayman al-Zawahiri to avenge the death of his deputy, Abu Yahya, who was killed in a drone strike in June.
A group called the “Imprisoned Omar Abdul Rahman Brigades”, which attacked both the Red Cross office and the US consulate in Benghazi earlier this year, was being put forward as a leading suspect for the attacks
One eyewitness told The Daily Telegraph that an armed group had infiltrated ordinary protesters who were already outside the consulate
US military officials said they were preparing to launch reconnaissance drones over eastern Libya to assist local security forces in hunting down the militants responsible for the consulate attack. The FBI was also reported to be involved in the investigation.
A senior Whitehall security official said many Islamist groups were still operating in the country with links with terrorist groups such as al-Qaeda, but that it was still too early to say whether the attack had been planned in advance.
The US was yesterday bracing for further flash points around the Islamic world as the controversial film, the “Innocence of Muslims”, which also provoked protests outside the US embassy in Cairo, spread virally across the Middle East on the internet.
However both Mr Obama and his secretary of state Hillary Clinton said that the actions of a minority of extremists would not derail on-going US-Libyan efforts to rebuild the country following the death and defeat of Muammar Gaddafi last year.
In an emotional tribute to one her best foreign service officers, Mrs Clinton said that Mr Stevens had “risked his own life to lend the Libyan people a helping hand to build he foundation for a new, free nation. He spent every day since helping to finish the work that he started.”
Mr Obama, who visited the State Department after speaking at the Rose Garden, said that the work that Mr Stevens had devoted and ultimately given his life for, would continue.
“This attack will not break the bonds between the United States and Libya,” Mr Obama said, “Libyan security personnel fought back against the attackers alongside Americans. Libyans helped some of our diplomats find safety, and they carried Ambassador Stevens’s body to the hospital, where we tragically learned that he had died.”