How to understand zone by MOMENT.js

I have problem with String > Format of timezone. I have string: " 2015-02-10 00:00:00,3,UTC " And try to format it in moment:

moment('2015-02-10 00:00:00,3,UTC', 'YYYY-MM-DD HH:mm:ss, ?, ?')

What should I insert instead of "?"