It can be rude anywhere, depending on the context. It's accepted as polite behaviour not to make eye contact in crowded underground/subway trains, for example.

Eye-contact is important for Russian speakers and it shows their attention to each other (like in other countries you mentioned before). It never could be considered as something rude or impolite. So eye-contact is a necessary part of everyday communication. On the other hand, if you don't know someone and he/she stares at you (and says nothing or tries to get acquainted with you but you don't want or don't need it ), it may seem impolite and annoying.

in mongolia , If this person is interested in you, create an eye contact