How do I loop over hosts identified by wildcards in Ansible?

Below is my playbook that works fine.

---
- hosts: "PROD_SERVERS"
  user: "{{ USER }}"

  tasks:

       - name: Check if all hosts are reachable
         fail:
           msg: "Server is UNREACHABLE."
         when: "hostvars[item].ansible_facts|list|length == 0"
         with_items: "{{ groups.PROD_SERVERS }}"

However, can you help me with the syntax when the host is presented as wildcard i.e {{ ENV }}_*?

---
- hosts: "{{ ENV }}_*"
  user: "{{ USER }}"

  tasks:

       - name: Check if all hosts are reachable
         fail:
           msg: "Server is UNREACHABLE."
         when: "hostvars[item].ansible_facts|list|length == 0"
         with_items: "{{ groups.{{ ENV }}_* }}" # <------- Need help with this part of the code

There are special variables also called as "magic variables" to identify the hosts in the current play. They are:

• ansible_play_hosts
• ansible_play_batch

You can use one of these variables to loop with instead of the inventory group name.

Example with ansible_play_hosts:

    - fail:
        msg: "Server is UNREACHABLE."
      when: hostvars[item].ansible_facts|list|length == 0
      with_items: "{{ ansible_play_hosts }}"

Update:

Changed the example for Ansible version "2.4.x", the loop should be performed with with_items rather than loop. Quoting from official documentation

We added loop in Ansible 2.5. It is not yet a full replacement for with_<lookup>, but we recommend it for most use cases.

Note: For Ansible "2.9.16" and "2.10.2" loop works as well.