Greek Unicode with markdown

I am using Calibre 5.37.

I have a markdown document which is a mix of English and Greek in unicode.

If I add it to Calibre and then view it with the book viewer the Greek letters show as diamonds. If I try to convert it needless to say the epub shows diamonds too.

If I take the markdown document and paste it into a Libreoffice document save it and if I add it to Calibre and convert it to epub both the English and Greek show fine.

Is there a way to import the markdown directly? Rather than having to convert it to odt first?

Thanks.