* Head of Libyan assembly says 50 suspects detained
* Interior minister says four held, 50 wanted
* Assembly head says consulate attack "planned by foreigners"
* Minister says consulate guards may have been infiltrated
WASHINGTON/TRIPOLI, Sept 16 (Reuters) - The head of Libya's national congress said on Sunday about 50 people had been arrested in connection with a deadly attack on the U.S. consulate in Benghazi last week, although the interior minister put the figure far lower.
Tuesday's attack in Benghazi coincided with protests over a video made in the United States that denigrates the Prophet Mohammad. It resulted in the deaths of the U.S. ambassador to Libya and three other Americans.
Libyan assembly head Mohammed Magarief was asked by the "Face the Nation" programme on the U.S. television network CBS how many people had been arrested in connection with the assault, and replied: "About 50."
But Libyan Interior Minister Fawzi Abdel A'al, when asked about that figure, told Reuters in Tripoli that only four arrests had been made and around 50 people were "wanted for investigation".
"What I have is that four have been arrested," he said.
Magarief said some of those arrested were not Libyans and were linked to al Qaeda, the militant Muslim group that carried out the Sept. 11, 2001, attacks on the United States.
Magarief, who became president of the national assembly last month after the bloody U.S.-backed overthrow of Muammar Gaddafi, described others as affiliates or sympathizers.
"It was definitely planned by foreigners, by people who entered the country a few months ago and they were planning criminal acts since their arrival," he said, adding that some were from Mali and Algeria.
He said the security situation in Libya remained "difficult" for Americans, as well as for Libyans. The United States wants the FBI to investigate the consulate attack, but Magarief said it may be too soon to send in investigators.
"It may be better for them to stay away for a little while until we do what we have to do ourselves," he said.
Magarief said there was little doubt the assault was planned rather than a spontaneous reaction to the video, citing the fact that it came on the 11th anniversary of the 9/11 attacks.
"These ugly deeds, criminal deeds, directed against late ambassador Chris Stevens and his colleagues, do not resemble in any way, in any sense, the aspirations, feelings of the Libyans toward the United States and its citizens," he said.
Abdel A'al said there were indications that the initial protesters had been armed.
The U.S. ambassador to the United Nations, Susan Rice, said on Sunday talks shows that preliminary information indicated that the consulate attack was not planned.
"There's no question, as we've seen in the past with things like 'The Satanic Verses,' with the cartoon of the Prophet Mohammad, there have been such things that have sparked outrage and anger and this has been the proximate cause of what we've seen," she said.
After the consulate was attacked, embassy staff were taken to a "safe house", where a second attack took place.
Asked how attackers managed to launch the second assault, Abdel A'al said: "I think there may have been an infiltration within the group protecting the consulate.
"This will come out in the investigation but there are indications that this is a possibility."