PHP：将多字节字符串拆分为没有空格的字符

How to split this string 'هذا   مثال' into seperate characters without whitespace using preg_split or mb_split?
I'm trying to split with preg_split('//u', $str, NULL, PREG_SPLIT_NO_EMPTY) but not to remove whitespace.

I want the following result: (remove space without using preg_replace or str_replace)

Array
(
    [0] => ه
    [1] => ذ
    [2] => ا
    [3] => م
    [4] => ث
    [5] => ا
    [6] => ل
)

$chars = preg_split('/[\.\s]?/u', $str, NULL, PREG_SPLIT_NO_EMPTY);