What kind of flame is this, that comes from the midst of a city, and devours the corner of  country?

Jeremiah 48:45 They that fled stood under the shadow of Heshbon because of the force: but a fire shall come forth out of Heshbon, and a flame from the midst of Sihon, and shall devour the corner of Moab, and the crown of the head of the tumultuous ones.

Also, what is the force that is mentioned?

And, who are the tumultuous ones?