Yes. However, an agency User Administrator may manage partner users where the partner has mechanisms *only* with your agency in your OU. If the partner has mechanisms with more than one agency in a country, then that partner's users cannot be managed by any of the agencies in that country. They can still be managed by interagency User Administrators.
Please note that all partners may also manage their own users, provided one of the partner users has been designated as a User Administrator.