WASHINGTON -- U.S. and Libyan officials are giving significantly different accounts of the gunfire and rocket-propelled grenade attack on the U.S. consulate in Benghazi that killed the U.S. ambassador to Libya and three other Americans.

The Obama administration says the assault was a spontaneous local reaction inspired by a demonstration that was taking place at the U.S. Embassy in Cairo against a video made in the United States slurring the Prophet Muhammad, the founder of the Islamic faith. It also contends that the attack grew out of a small protest.

A senior Libyan official says the attack was organized and planned by foreigners – some with links to al Qaida – involved a local Islamic militia, and was timed for the anniversary of the Sept. 11, 2001, terrorist attacks on the United States. Moreover, the Libyan official appeared to question whether there was a protest beforehand.

“The way these perpetrators acted and moved, and their choosing a specific date for this so-called demonstration, I think that this leaves us with no doubt that this was pre-planned, pre-determined,” Mohammad Magarief, the head of the Libyan National Congress, the recently elected interim government, said Sunday.

The drastically different versions come as the investigation into the assault still is in its preliminary stages. FBI agents who are to assist their Libyan counterparts have yet to arrive in the North African country, and the Libyan Interior Ministry official who was in charge of the investigation was fired Monday.

Both governments would have good reason to promote their version of the incident.

Libya’s factionalized and weak interim government is confronting growing violence by militias and Islamic extremist groups that refused to disarm after overthrowing the late dictator Moammar Gadhafi last year. The interim government would appear less ineffectual and feckless if the attack were a deep-rooted conspiracy by the world’s most feared terrorist network.

President Barack Obama’s claims that he has kept Americans safe from terrorism and dealt debilitating blows to the remnants of al Qaida have been centerpieces of his appeal for re-election in November. Those claims could be questioned by GOP candidate Mitt Romney and other Republicans if al Qaida is found to have planned a well-coordinated attack on such a significant date without being detected by U.S. intelligence.

The attack claimed the lives of U.S. Ambassador to Libya Christopher Stevens, who was visiting Benghazi from the capital of Tripoli, Sean Smith, an information technology specialist, and two security men, Tyrone Woods and Glen Doherty, both former Navy SEALs.

Scores of attackers firing assault rifles and rocket-propelled grenades charged the walled compound from two directions, swarmed inside and attacked the main building, setting it afire, witnesses have told McClatchy. Stevens and Smith apparently died from smoke inhalation. Woods and Doherty were shot dead protecting up to 30 U.S. staffers who had taken refuge in a nearby annex.

The consulate compound’s landlord, Mohammed al Bishari, and a 27-year-old guard, who was wounded and asked to remain anonymous, told McClatchy last week that no protest was taking place when the attack was launched at 9:35 p.m. local time. They described the assault as sudden and well-coordinated.

The assailants were carrying the black flag of a local Islamic extremist group, Ansar al Shariah, Bishari said.