Four people were killed in Nigeria after assailants attacked a convoy carrying U.S. and Nigerian officials, the State Department confirmed on Wednesday.

“We condemn in the strongest terms this attack,” Secretary of State Antony Blinken said in a statement. “We will work closely with our Nigerian law enforcement colleagues in seeking to bring those responsible to justice.”

The assailants attacked the convoy on Tuesday. It included five U.S. Embassy officials and four members of the Nigeria Police Force, in the Ogbaru Local Government Area of Anambra state.

The State Department did not provide the nationalities of those killed, but The Associated Press said they were two of the Embassy’s “local workers” and two police officers.

A motive for the attack is still unclear, but there is “no indication” the U.S. officials were intentionally targeted, the State Department said. The region is the site of intense separatist violence, according to the AP.

“The United States has no greater priority than the safety and security of our personnel,” Blinken added in his statement. “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.”