false-flag

Noun

false flag (plural false flags)

1. A ruse, in the days of sail, in which an attacking ship would fly the colours of its enemy until close enough to open fire.
2. A diversionary or propaganda tactic of deceiving an adversary into thinking that an operation was carried out by another party.
   • Using what the bureau calls a "False Flag" operation, F.B.I. agents posing as Russian intelligence officers contacted Mr. Pitts in August 1995, long after it believed he had ceased his spying activities, and feigned interest in reactivating him as a means of confirming his spying activities and...1996 December, David Johnston, “F.B.I. Supervisor Charged With Spying for Russians”, in The New York Times

See all 3 meanings of false flag