The US announced it will provide $5m (£3.1m) to Nigeria and its neighbouring countries engaged in a joint offensive to halt terror group Boko Haram.
The state department official added that the US is already providing $34m (£21.6m) to Chad, Niger and Cameroon for logistics and other equipment, Reuters reported.
The country is also to send military trainers to help the Nigerian army improve its intelligence gathering and logistics.
The Nigerian government is being aided by mercenaries and troops from Chad, Benin, Niger and Cameroon in its offensive and has scored some successes since the military cooperation started in February.
Newly elected President Buhari, a former military chief, vowed Nigeria would do anything it can to defeat the deadly insurgence and find some 220 girls who were kidnapped by Boko haram in Chibok, Borno state, in April 2014.
The US announcement came hours after at least eight policemen were killed in a bomb attack in Damboa, Borno.
Boko Haram is also suspected of being behind a terror attack that occurred outside the police headquarters and academy in Chad's capital N'Djamena that killed dozens of people in June.