angular2 group of checkboxes with required attribute

i want to create a template-driven form in Angular2 (RC5), that will include a group of check-boxes, bounded to specific attributes of an object. Right now, i have such group, bounded to the corresponding array like:

<div class="checkbox" *ngFor="let prop of properties">
  <label>
    <input type="checkbox" name="option" id="option [(ngModel)]="prop.state"/> 
    
  </label>
</div>

Although this is pretty straightforward, i cannot figure out how to add a required attribute to this group of check-boxes. What i mean by that, is that i need to force user to select AT LEAST one of the group check-boxes, otherwise form validation will fail.

Any ideas?