Invoking multiple playbooks with include inside a block of Ansible

I am trying to have a block in Ansible which will invoke multiple playbooks using include if a specific flag is set. I am trying to achieve something similar to below:

- hosts: localhost
  tasks:
   - block:
      - include: script1.yml
      - include: script2.yml
      - include: script3.yml
     when: flag|bool

This snippet throws an error stating ERROR! unexpected parameter type in action: <type 'bool'>

Thanks in advance!