So far, the group's presence in the kingdom appears to be in a low-level stage, but it has claimed four significant bombings since May, one of them in neighbouring Kuwait.
For two decades, Harvard Law School has had its own Islamic legal studies program, established with support from the Saudi king.
The Saudi embassy has dismissed the charges against the diplomat as "completely false" and "contrary to facts in our possession"
The latest victims were two expatriates aged 44 and 57 and a 67-year-old Saudi national, the health ministry said.
The Al Sabeen maternity and children's hospital said it had been damaged and appealed to international organisations to help evacuate them.