The Prime Minister wrote in The Sunday Telegraph this weekend that the group posed a "deadly threat" to the UK, adding that a "humanitarian response" was not enough.
However, despite stating that Britain should use its "military prowess" he later insisted there would not be "boots on the ground", and that troops would not be sent into Iraq as they were in 2003.
Cameron’s words follow the UK providing aid for Yazidi refugees who fled to Mount Sinjar following persecution by IS.
How I See It
Gavin Megaw, director, Hanover
How do you demonstrate leadership without inadvertently putting boots on the ground? That has been David Cameron’s challenge as the world faces a growing threat from Islamic State fundamentalists.
As soon as he headed on a now cut-short holiday (as if a PM actually gets a break), the Mail and Sun attacked him for doing so while Iraq and Syria burned. The coverage led some to recall a famous quote from Edmund Burke: "The only thing necessary for the triumph of evil is for good men to do nothing."
Cameron had to do something, so he drew a line in the sand. First, he talked tough to Middle England via a Telegraph interview. He said IS posed a "direct and deadly threat" and Britain had "no choice but to rise the challenge". Yet, when questioned on BBC Breakfast, he refused to go beyond that – ruling out a war in Iraq.
He is walking a tightrope; the Westminster Village wants to know his plans, yet it makes no political or militarily operational sense to go further at this stage. He is damned if he does and damned if he doesn’t.