Automatic calling system: "Press star" or "Press asterisk"?

I'm not a native English speaker and currently have a task on my desk to translate some texts for an automatic telephone calling system. You know the stuff: to confirm your request, press one, to cancel, press pound.

And the question is: Should I use "star" or "asterisk", down left on the keypad, when your computer program talks to someone over phone?

Edit:

The calling system will be addressing both native English speakers and people who have English as their second or third language.

Asterisk is easier to understand in over low-quality telephone connection, but may confuse non-native English speakers.

Star is more or less clear to everyone, but may get misheard as it is only one syllable (especially when the phone connection is suboptimal).

Edit 2:

The system is supposed to give calls to people around the world in case of emergency with system they are responsible for. It allows for translation to any language, but the company running the system will not pay translation for one or two people, so everyone for whom there is no translation will get the call in English.

We use software synthesized voice messages (and not recorded human voice) and so the messages need to be as clear and concise as possible.