Thank you for the reply,
It doesn't seems like that. In MS Word I can create two tables without a paragraph in the middle and this is confirmed by the document.xml inside it (I have not modify directly the document.xml); the code that I quoted is copied and pasted from it. So it seems possibile!
I tried your solutions and it works, it's just a little bit odd because, obviously, inside the docx this paragraph is visible, without it would be cleaner
Thanks, Federico