US Secretary of State Antony Blinken testifies during a Senate Appropriations Committee hearing on the 2024 proposed budget request, focusing on investing in US security, competitiveness, and the path ahead for the US-China relationship, on Capitol Hill in Washington, DC, on May 16, 2023.
"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.
Blinken, confirming Nigerian police accounts, said that the attack Tuesday in the southeastern Anambra state killed "at least" four people.
The two-vehicle convoy was carrying nine people, all Nigerians -- five working for the US government and four police officers.
Blinken said that the convoy was traveling to prepare a visit to a US-funded flood response project.
"We do not yet know the motive for the attack, but we have no indications at this time that it was targeted against" the embassy specifically, he said.
Saluting the role of local staff, Blinken said, "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."
Nigerian officials often blame attacks in the southeast on the outlawed Indigenous People of Biafra movement and its armed wing, the Eastern Security Network.
More than one million people were killed in Nigeria in a three-year civil war following the declaration of an independent Biafra Republic in the southeast by Igbo army officers in 1967.
Separatists still operate in the country's southeast, where they have escalated their attacks in recent years, usually targeting police or government buildings.