Convert UTF8 csv file to xls in headless mode

I use the following command (Mac OSX) to convert a UTF8 csv file to xls file, work fine, except when there is character out of the ASCII range, it become messy…

/Applications/LibreOffice.app/Contents/MacOS/soffice --headless --convert-to xls:"MS Excel 97" utf8.csv

Are there any way to make the conversion work fine for UTF8 also? Thanks.