Such operations that are referred to as ‘suicide operations’ or intihari operations have no place in the Shia culture and aren't permissible per se. Nevertheless, if the precious religion of Islam is ever threatened by a great threat, and there is no other choice to relieve it of these threats, such that the protection of Islam solely lies in such operations, it will become a kifa’i wajib act (meaning that it is wajib upon all Muslims, unless the needed number of people take care of the task) with the permission of the Hakem Shar’, given that innocent lives aren't lost in the process.
 Please pay attention to these inquiries from the offices of the maraje’:
The office of the Grand Ayatullah Khamenei:
It is impermissible.
The office of the Grand Ayatullah Sistani:
Ayatullah Sistani hasn’t issued such a ruling till now and such a thing can't be found in the Shia culture.
The office of the Grand Ayatullah Safi Golpaygani:
If the only way to protect Islam is through such operations, it is a kifa’i wajib. Nevertheless, the term shahid covers more than just those shahids who don’t need to be given ghusl and shrouded [such shahids who have lost their life via suicide operations still need ghusl and the shroud, but still are shahids].
The office of the Grand Ayatullah Makarem Shirazi:
Suicide operations are impermissible, except for when a danger threatens Islam and there is no way to protect it except through suicide operation; in such a case it is permissible but with the permission of the Hakem Shar’.