WASHINGTON - US authorities are investigating possible collusion between militants who launched a deadly attack on the U.S. consulate in Benghazi, Libya and locally hired Libyan personnel guarding the facility, three US officials said.

So far there is no proof that the attackers, who killed US Ambassador Christopher Stevens and three other US officials, were helped by Libyan security personnel hired by the consulate. One official said the Obama administration was playing down this possibility.

However, all the officials said that the question of whether the attackers had inside help or advice was a serious issue in the US investigation into the attack, which occurred on the 11th anniversary of the Sept. 11, 2001 attacks on the United States.

A team of FBI investigators has gone to Libya to lead the investigation.

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