Can A Ford 3000 Radio Support Rear Speakers?

Hi.
I currently drive a P reg ford fiesta and it is fitted with a standard ford 3000 stereo/cassette unit.
I am looking to purchase speakers for the car, to be positioned in the rear, as i already have speakers in the front doors but would like to increase the in-car entertainment factor. I was wondering if the stereo unit could support two more speakers at all? as i have heard mixed opinions.
And also if not, any suggestions as to how i may accomplice adding two more speakers to my car?

Many Thanks