How to include external html file and js file in polymer 3?

I am trying to separate html part from .js in polymer 3.0 . How can I include external html file in .js ? OR how can I separate them ?

import {html, PolymerElement} from '@polymer/polymer/polymer-element.js';
/**
 * @customElement
 * @polymer
 */
class InfyAssign extends PolymerElement {
  static get template() {
    return html`
    <style>
    :host {
      display: block;
    
    }
  </style>
  <div class="row">
  <div class="col-md-3">
      Hello
  </div>
    <div>
      <img src="../../images/image1.jpg">
    </div>
  </div>
 
    `;
  }