Is it possible to place a die into a large city without doing the relative action, just to deny it to another player?
Rules say you can use the action a number of times up to the number of die placed, I don't know if zero is an available choice.
In addition to what Alan said, p6 in the English rules state (emphasis mine)
* If you are allowed to perform an action out multiple times or get more from the action, you can always choose to perform the action out fewer times or get less. You must always perform the action at least once.