A full-blown political offensive is being ramped up in the tiny Gulf nation with big fault lines: US-allied Sunni rulers against members of a Shiite majority being cast as coup plotters who could open the door to Iranian influence.

On Sunday, Bahrain's King Hamad bin Isa Al Khalifa gave a national address to decry 'strife, aggression and terrorism' and announce plans for greater government monitoring of 'religious forums' - an apparent reference to Shiite clerics and others.

A day earlier, state media released the photographs of 23 Shiites - ranging from opposition figures to professors and taxi drivers - accused of conspiring to overthrow the government. They include opposition leader Abdul-Jalil al-Singace, arrested August 13.

Rights groups say more than 250 Shiites have been detained.