I have done it before in games, but I am not 100% positive. A quick check of the rules thread seems to suggest you cannot, though.
@zhavier weighing in early on with no objection
@mysticjuicer and @Legion weighing in last fall with no objection
Even so, I think I was pretty well cooked.
It would be worth having definitive weigh-in whether attacking your own units is allowed or not from the rulebook or @sharpobject / @Leontes / @Sirlin / other staff, though!