Who can initiate an optional referendum at the national level?

Constitution 1992

Article Twenty five

1. The State Ikh Khural may consider on itsinitiative any issue pertaining to domestic and foreign policies of the State,and shall keep within its exclusive power the following issues and decidethereon:

[…]

16) to hold national referenda. To verify the validityof a referendum in which the majority of citizens eligible for election hastaken parts, and to abide by and give effect to the decision which has obtaineda majority of votes;

Article Sixty eight

l. Amendments to the Constitution shall be initiatedby organization and officials enjoying the right to legislative initiative andcould be submitted by the Constitutional court to the State Ikh Khural.

2. A national referendum on constitutionalamendment may be held on the concurrence of not less than two thirds of themembers of the State Ikh Khural. The referendum shall be held in accordancewith the provisions of sub-paragraph16 of Paragraph 1, Article 25 of the Constitution.