Iran on Saturday underlined the seriousness in avenging the death of its commander Qassim Suleimani by unfurling the symbolic red flag at a mosque in the Shiite holy city of Qom. Red flags in Shiite tradition symbolize both the blood spilled unjustly and serve as a call to avenge a person who is slain.

from Times of India https://timesofindia.indiatimes.com/world/middle-east/iran-hoists-red-flag-on-mosque-to-avenge-killing-of-commander-qassim-suleimani/articleshow/73106490.cms