fan the flames
Intensify or stir up feelings; exacerbate an explosive situation. For example, She already found him attractive, but his letters really fanned the flames, or His speech fanned the flames of racial dissension.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.