She spoke during a media briefing in Abuja on Monday.
Leonard said partnering Nigeria to identify sponsors of Boko Haram was something the U.S. was very eager to do.
She said had had at least three conversations in the last two months on this subject, but said she would not go into details.
Leonard, however, said that the induction of the A-29 Super Tucanos, was a significant milestone in the US.-Nigerian bilateral relations.
She added that the U.S. had remained committed to support Nigeria fight insecurity.
Leonard said the U.S. government was also committed to supporting democracy and economic programmes of the government through the embassy.