set the center of a embedded map (google map) to a specific location

I'm trying to use this map in a website and I am using the next pieace of html code to add it.

<iframe src="http://ift.tt/1Ag5jwC" width="640" height="480"></iframe>

My problem is that I want the embedded map to show the Utrecht area only, but I can't figure out how to change the center of the embedded map. I know that the parameter z= will set the zoom level. I've tried the center= parameter as specified in the documentation, but it does not seem to work

http://ift.tt/1yd6OgR

does anybody how to set the center?

Thanks in advance!