Most of them / most of whom

Army officials there says all 20 people taken hostage and killed by their captors in an attack on a cafe in the capital, Dhaka, were foreigners, most of them Italian or Japanese.

Is the sentence natural to you?

I think that ,and most of them are or ,most of whom are should be put and I think that are also cannot be omitted.

What do you native English speakers think?

Thank you so much as usual in advance.