As Basil wrote, Hamas may not be the party who fired the rockets. But it doesn't make any difference. Hamas claims to rule Gaza. If other parties fire rockets, Hamas is still responsible. If Hamas is incapable of stopping other parties then Hamas does not in fact rule. Ruling means being in charge. If Hamas is not completely in charge, then it is not the ruling party.
Iraqi car bomb death toll rises to 25 (Reuters)
from the article: Israel warplanes strike Hamas targets following Gaza rocket fire