Who can initiate an optional referendum at the national level?

Belize
Section 2
(1) Without prejudice to any law which provides for a referendum to be held on any specific issue, the National Assembly may by resolution passed in that behalf declare that a certain issue or matter is of sufficient national importance that it should be submitted to the electors for their approval through a referendum.
(2) Notwithstanding subsection (1) above, a referendum shall be held on the following issues:-
(a) any amendment to Part II of the Constitution which derogates from the fundamental rights and freedoms guaranteed therein; and
(b) any proposed settlement with Guatemala for resolving the Belize/Guatemala dispute.