"Certain places" as in "Mecca"? You realize then you just gave a motive to anyone who wants Mecca destroyed, right? I don't think naming "certain places" does much good, and possibly more harm, than you would think.
They already want to die as martyrs, fear of their own death is useless. Fear of reprisal against most cities and countries would be acceptable damages.
So what would make them fear a big hit against us? I am open to ideas.