KABUL, June 8 (Reuters) - The United Nations mission in Afghanistan has expressed concern over the arrest and detention of women in a western province for allegedly failing to comply with "dress requirements" and urged Taliban authorities to treat all people equally. The United Nations Assistance Mission in Afghanistan (UNAMA) did not specify how many women had been affected, though local media reported last week that at least 21 women and girls were detained in Herat province. The Afghan Taliban did not respond to Reuters request for comment.