U.S. intelligence officials, speaking with NBC News on condition of anonymity, declined to characterize the nature of the evidence, other than to say it was recent and non-specific. But they said it is prompting efforts to locate the terrorist group’s “military assets” and identify other senior leaders beyond Abubakar Shekau.

They also said that Boko Haram’s desire to strike against a U.S. target apparently has been heightened by the increasing U.S. involvement in the hunt for 276 missing Nigerian schoolgirls abducted by the group last month, though the goal itself is not new.

“Boko Haram has a long standing interest in this,” said one senior U.S. counterterrorism official when asked about the possibility of an attack. “… It’s consistent with what we’ve seen from them. Broadly speaking, it’s in line with what we are tracking.”