(CBS News) South Carolina Republican Sen. Lindsey Graham called Monday for a congressional investigation into last week's deadly assault on a U.S. Consulate in Libya amid an apparent disagreement between American and Libyan officials on how much planning went into the attack.
Graham voiced his agreement with Libyan President Mohamed Magariaf, who said on CBS' "Face the Nation" Sunday that the execution of the attack. The Obama administration has called the attack more impulsive than planned.
"The Obama Administration's insistence that the attack on our consulate in Benghazi, Libya resulted from a riot inspired by a film, rather than a planned and coordinated attack, defies common sense," Graham said in a statement.
The FBI has already launched an investigation into the attack, which killed U.S. Ambassador Christopher Stevens and three other Americans.
"It was planned, definitely, it was planned by foreigners, by people who entered the country a few months ago, and they were planning this criminal act since their arrival," Magariaf told Bob Schieffer Sunday.
Graham's comments come on the heels of other Republican lawmakers who believe the attack was planned. Sen. John McCain, R-Ariz.,that "most people don't bring rocket-propelled grenades and heavy weapons to demonstrations." Last week, House Intelligence Committee Chairman Mike Rogers, R-Mich., told CBS News Capitol Hill producer Jill Jackson the assault "clearly was a designed attack."
But U.S. Ambassador to the United Nations Susan Rice told Schieffer that, so far, the United States' investigation shows the attack stemmed from "spontaneous protests" against an American-made online video ridiculing Islam.
"It looks like extremists elements joined in that effort with heavy weapons ... and it spun from there into something much, much more violent," Rice said.
CBS News national security correspondent David Martin reports Ansar al Sharia, a radical Islamic group,, according to U.S. officials. The officials describe the group, whose name means "Supporters of Islamic law," as an offshoot of al Qaeda.
Hours after Tuesday's attack, Wanis al-Sharef, a Libyan Interior Ministry official in Benghazi, told reporters that Americans "should have taken more appropriate security measures." Al Qaeda chief Ayman Al-Zawahri called on Muslims the day before to avenge the death of Abu Yahya al-Libi, a top Qaeda commanderin June.
Tuesday's attack wasn't the first on the Benghazi compound.
In June, a bomb exploded outside the consulate, the first act of retribution for the al-Libi killing. The SITE monitoring service reported that the Brigades of imprisoned Sheik Omar Abdel-Rahman, a militant group, claimed responsibility for the bombing, according to The Associated Press.
A week later, two bodyguards were injured in Benghazi in an attack on U.K. Ambassador Dominic Asquith's car.
In August, after regional Salafist Muslim groups destroyed at least two historical religious shrines in Libya, Interior Minister Fawzi Abdelaliand admitted the government was powerless to stop the militants.
"If we deal with this using security we will be forced to use weapons, and these groups have huge amounts of weapons," he said. "They are large in power and number in Libya. I can't enter a losing battle."
Ansar al-Sharia, which has said it participated in but did not plan Tuesday's attack, has such power in the city that the group released photos in August showing its black-clad militants riding in a convoy of vehicles - which look almost like official police vehicles emblazoned with their logo - through Benghazi's streets. According to the statement posted to the group's Facebook page along with the photos, Ansar al-Sharia was taking responsibility for the security of one of Benghazi's major hospitals.
Tucker Reals contributed reporting from London.