M., it sounds like he needs a different motivator. I've actually decided to try this when my little one is old enough.
I'd start by asking him why he gets so mad that he wants to hit and kick his friends. Then I'd help him empathize with the other kids and ask him how he'd feel if they hit or kicked him.
He probably also needs help discovering a healthy means of dealing with his anger, like practicing counting slow, deep breaths. Ideally, it should be something he can easily do, he likes to do, and something he can be easily reminded to do until it becomes a habitual way of calming down. He might even need suggestions about what words to use with his friends when he's feeling the anger.
I'd then shift the focus from the negative (things taken away for bad behavior) to the positive (good behavior earns extra privileges). Seeing his progress will encourage him, so I might try a reward system instead of a punishment system. You could decide on a treat he really enjoys (time at the park, an extra book at bedtime one night, etc). and let him earn it weekly.
Get him his own "good behavior" calendar and let him put a star on each day that he doesn't act out against other kids. Set a number of stars he has to earn to get his weekly reward. As he improves, you might encourage him to do even better and increase the number of stars required, or even change the frequency of the reward from weekly to monthly. (If it's a monthly reward, I'd make it a littler bigger, like going to see a movie or having a friend stay the night).
Get excited about the good days and don't dwell on the bad days - the less attention bad behavior gets, the more likely he will be to seek out the positive attention he gets when he behaves well.
Good luck!