How to automatically kill sessions after deleting or disabling a policy?

I’m deleting (or disabling) a firewall policy, but the sessions that were created under that policy remain active.
firewall-session-dirty is set to clear-all. But it doesn’t clear the existing sessions.

Is there any way to make FortiGate automatically terminate sessions when a policy is disabled or deleted?
Or is manual session clearing (e.g. via diagnose sys session clear) the only option?