Shaykh Saalih al-Fawzaan was asked:

Esteemed Shaykh, may Allaah grant you success, are those who performed bombings in this country considered to be bughaat (transgressors) or khawaarij (revolters)?

His response:

They are more severe than the Kharijites, the Kharijites did not do the likes of this act. So they are Kharijites and something additional (on top of the Kharijites), they added (more to what the Kharijites did). The Kharijites did not enter upon the people in houses and demolish them ontop of them and kill children and whomever they find. The Kharijites (of old) did not do this, only the Qaraamitah, this act (of the contemporary Kharijites) resembles the act of the Qaraamitah.

Note: The Qaraamitah were an extreme sect who killed Muslims and attacked the Ka'bah, and they concealed disbelief whilst manifesting belief.

Source: The source of this can be found in this audio at the 7:00 mark onwards.