Dubai - Washington ordered all non-essential staff to leave Tunisia and Sudan after its embassies were stormed by Muslims protesting an anti-Islam movie and as al-Qaeda called for more attacks on US targets.
US officials have already deployed counter-terrorism Marine units to Libya and Yemen and stationed two destroyers off the North African coast.
But Sudanese Foreign Minister, Ali Karti, on Saturday flatly rejected a US request to send special forces to protect the Khartoum embassy, the official SUNA news agency said, quoting his office.
Hours later, US officials announced Washington would evacuate all non-essential staff and family members from Sudan and Tunisia and warned US citizens against travel to the two countries.
Despite Tehran's hostility to Washington and its own condemnation of the movie, Iran's Revolutionary Guards commander General Mohammad Ali Jafari said the killing of the US ambassador to Libya last Tuesday was unjustified.
"Definitely this did not warrant killing," Jafari told a news conference in Tehran. He said that "due to their anger (of protesters), this incident (the killings) happened."
In the worst violence sparked by the film, the US ambassador to Libya, Chris Stevens, and three other Americans died when suspected Islamic militants fired rocket-propelled grenades at the US consulate in the eastern city of Benghazi.
In cities across the Muslim world protesters have since vented their fury at the Innocence of Muslims - an amateur film produced in the United States - by targeting symbols of US influence ranging from embassies and schools to fast food chains.
With Muslim anger boiling, al-Qaeda in the Arabian Peninsula (AQAP) on Saturday issued a call for more violence against US diplomatic missions in the Middle East and Africa, and urged attacks on US interests in the West, the SITE Intelligence Group said.
AQAP, al-Qaeda's Yemeni offshoot, did not claim direct responsibility for the deadly attack in Benghazi.
But it said the killing of al-Qaeda deputy leader Sheikh Abu Yahya al-Libi in a June drone strike in Pakistan "increased the enthusiasm and determination of the sons of (Libyan independence hero) Omar al-Mukhtar to take revenge upon those who attack our Prophet," according to SITE.
Lieutenant Colonel Hagen Messer conceded that the scale of damage, carried out by more than a dozen attackers dressed in US Army uniforms and armed with guns, rockets and suicide vests who managed to storm the airfield, was unprecedented.
Friday's attack came after at least 11 protesters died as police battled to defend US missions from mobs in Egypt, Lebanon, Sudan, Tunisia and Yemen.
US Defence Secretary Leon Panetta said Washington was configuring its forces to cope with the widespread violence.
"We have to be prepared in the event that these demonstrations get out of control," Panetta told Foreign Policy magazine.
On Friday, guards on the roof of the US embassy in Khartoum fired warning shots at protesters who breached the compound walls waving Islamic banners. The same group had earlier ransacked parts of the British and German missions.
A similar assault mostly by hardline Islamists on the American embassy in the Tunisian capital on Friday ended with four people dead and 49 injured.
In the past week, US embassy compounds have also been breached in Egypt and Yemen, whose parliament rejected the presence of US Marines although the government has already accepted them.
A planned demonstration against the deployment of the Marines in Sanaa was called off on Sunday after people failed to show up, an AFP correspondent at the scene reported.
The head of Libya's national assembly, Mohammed al-Megaryef, said foreign elements may have been involved in the "meticulously executed" attack on the US consulate in Benghazi.
It came on the anniversary of the 11 September 2001 terror attacks on the United States.
US Secretary of State Hillary Clinton undertook a round of telephone diplomacy Saturday, calling her counterparts in Egypt, Saudi Arabia, Turkey, Britain and France, as well as the prime minister of Libya and the Somali president, in a bid to rally support, State Department spokeswoman Victoria Nuland said.