The United States carried out airstrikes against Daesh-linked terrorists in northwestern Nigeria, President Donald Trump said Thursday, marking a sharp escalation in U.S. involvement in a security crisis that has overwhelmed Africa’s most populous nation for years.

In a Christmas evening post on social media, Trump described the operation as a “powerful and deadly” strike against fighters he said were “targeting and viciously killing, primarily, innocent Christians.”

He offered no details on casualties or damage, and U.S. officials did not publicly identify the specific terrorist group targeted.

A Defense Department official, speaking on condition of anonymity because details had not been made public, said the strikes were carried out in coordination with Nigeria and approved by its government.

Nigeria’s Ministry of Foreign Affairs confirmed the cooperation, saying it involved intelligence sharing and strategic coordination “consistent with international law, mutual respect for sovereignty and shared commitments to regional and global security.”