Four people were murdered when assailants, whose identity and motive remain unknown, attacked a convoy of United States government vehicles in Anambra, Nigeria, on Tuesday.

Two U.S. government vehicles, carrying nine Nigerian nationals, including five that work for the U.S. Mission to Nigeria, were traveling in advance of a planned visit by U.S. Mission personnel to a U.S.-funded flood response project in Anambra. That is when the assailants attacked, according to a Wednesday update from Secretary of State Antony Blinken.

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He said they "do not yet know the motive" behind the "unknown assailants" attack.

At least four members of the convoy were killed, while an unknown number are unaccounted for at this point. The four individuals in the convoy who were not working with the U.S. Mission were members of the Nigerian Police Force.

The attackers “murdered two police operatives and two staff of the U.S. Consulate and set their bodies and their vehicles ablaze," the Anambra Police Command told CNN.

"We condemn in the strongest terms this attack. We will work closely with our Nigerian law enforcement colleagues in seeking to bring those responsible to justice," Blinken said in a statement. "The United States has no greater priority than the safety and security of our personnel. We express our heartfelt condolences to the families of those killed in the attack, and pledge to do everything possible to safely recover those who remain missing. We deeply value our relationship with our Locally Employed Staff and our partnership with Nigeria."

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A day earlier, national security council coordinator John Kirby told reporters that, "No U.S. citizens were involved, therefore, there were no U.S. citizens hurt."