That's interesting! From my (admittedly very weak) understanding of Cyrillic, I'd expect Беларусь to be pronounced with a "y" sound as part of the "e", similarly to the vowel at the start of Ельцин (Yeltsin).

Presumably that's because of a lack of orthographic knowledge on my part... or is it something more subtle (say, the belorusian language differing from Russian)? I have a vague memory of languages in the former Yugoslavia being either "ekavsky" or "ijekavsky".