Exchange of fire took place during operation to clear suspected militants from tribal agency.
At least three Levis personnel injured after IED detonates in Dabar.
Improvised explosive device targeted school van, killing teachers and students.
Arshad Khan removed from office, as military prepares to expand operation into Bajaur Agency.
No claims of responsibility thus far for the separate IED detonations.
Spokesman for militant group alleges government is powerless to negotiate peace, and claims shelling in North Waziristan is targeting civilians.