There are variants in which the prepositive negation ne is used, while other variants use postpositive netu.
The negative marker always precedes modal and auxiliary verbs: ne mogu, ne nado etc.
Source: Neumann 1966: 246
Source: Arsen’ev 1949: 257
Source: Neumann 1966: 248
Source: Perekhvalskaya 2008: 237