The same way you ban pirated media from being downloadable on the Internet: not effectively.

Trade restrictions, sanctions. You can't effectively ban for individuals, but you can make it so legally risky for US based companies that it becomes effectively illegal as no US company will touch them, nor host them.

I'm old enough to remember "this shirt is a munition" and the DeCSS t-shirt.

In the same way you can for any digital information?

How do you ban melted sand?