Los Angeles police said they have not determined any credible threat to the city's buildings in connection with a social media post Friday.
LAPD did not specify or describe the posting, but multiple outlets referred to a photo depicting an explosion apparently photoshopped over a downtown Los Angeles building. A figure made to look like a member of a terrorist group overlooks the scene.
The agency said while it has found no evidence to suggest any real danger, investigators are taking the matter seriously and are working with federal officials to trace the source of the post.
"As always we encourage every Angeleno to heighten their awareness and 'if you see something, say something,'" LAPD tweeted.
Authorities provided no further details.