How can I avoid wrapping my block into  tags?
I think you should copy block.html.twig (perhaps from /core/themes/classy/block/block.html.twig) in your custom module/theme and make it work for your specific block by naming it block--BLOCKID.html.twig and remove the outer &lt;div&gt; from this twig file.

Alternativelly you can create a custom template