Story highlights The FBI's involvement is a routine step when US citizens are killed overseas

Another US official said FBI investigators are on the ground in Niger providing technical assistance

(CNN) The FBI is assisting Niger authorities in the investigation of the deaths of four US servicemen, a law enforcement official tells CNN, a routine step for the bureau when US citizens are killed overseas.

Another US official said FBI investigators are on the ground in Niger providing technical assistance and helping to gather and evaluate evidence related to the attack.

The investigators are based out of US embassies in nearby African countries, the official said, and reiterates the FBI role in Niger is not unprecedented, as the bureau often lends its expertise into terror investigations abroad.

The Wall Street Journal earlier reported the FBI's involvement.

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