Hello P.,
You can, see one example here:
But it is only currently on inline mode (awaiting the multi-line mode of Activity diagram), like:
@startuml
start
repeat :read data;
:generate diagrams;
repeat while (\n{{\nsalt\n{^"Next step"\n Do you want to continue? \n[Yes]|[No]\n}\n}}\n)
stop
@enduml
If that can help,
Regards,
Th.