Render comment edit form in block
I found a solution for this case, sharing so that anyone who need similar solution can use it.

Anyone who has similar issue can use the solution below:

&lt;?php       
    $comment = comment_load($comment_id); // $comment_id = cid of comment whose edit form need to be open

    module_load_include('inc', 'comment', 'comment.pages');
    $form = drupal_get_form('comment_form', $comment); 

    return drupal_render($form);
?&gt;