In theory, such bets run afoul of US financial rules, which bar trading on contracts involving war, terrorism, assassination, gaming or other illegal activities.
But that hasn’t stopped firms from taking in millions of trades.
Critics have seized on the activity, calling for a crackdown on the apps, which they say are facilitating unseemly, and potentially illegal, war profiteering, generating national security risks and enabling opportunities for insider trading and corruption.
“You have now opened up gambling basically on almost anything and it has turned into this very, very gruesome type of thing on the death of a head of state,” said Craig Holman, government affairs lobbyist at the Public Citizen advocacy group, which recently filed a complaint this week over the bets.
Polymarket alone has hosted what Bloomberg estimated as more than $500m in bets related to the Iran war, at one point offering an opportunity to play the odds on the chance of nuclear detonation.
The company, which is headquartered in New York but operates on a limited basis in the US, eventually removed that market after it drew scrutiny on social media but users can still submit bets on questions like when US forces will enter Iran. It did not respond to the BBC’s request for comment.
Kalshi also ended up cancelling the Khamenei market, which had drawn $54m in trades, noting that US-regulated entities are barred from “having a market directly settling on someone’s death”.
The company, which did not respond to a request for comment for this article, has said the war bets are happening on unregulated exchanges outside the US.