regexp and greek characters

[papas]

SELECT a.store_id, a.store_name, a.store_type, a.store_description, a.store_logo_path, b.cat_name
FROM tbl_stores a
LEFT OUTER JOIN tbl_store2categories c ON a.store_id = c.store2cat_store_id
LEFT OUTER JOIN tbl_categories b ON c.store2cat_cat_id = b.cat_id
WHERE a.store_name
REGEXP '^[Α-Δ]'
AND a.store_showstore !=0
GROUP BY a.store_name
ORDER BY a.store_name DESC
LIMIT 0 , 10


hello everyone

i have the above query that uses regexp to find all names that start lets say in english from a to d
but insted of ^[a-d] im using greek characters α-δ which dont seem to be working at all.
my db is utf8_unicode also i used mysql_query('SET NAMES utf8');

any ideas ?

thank you