The head of the Islamist Hamas movement in Gaza, Yehya al-Sinwar, says its fighters have inflicted heavy losses of life and equipment on Israeli forces in the conflict. In a letter to the chairman of the Hamas politburo, Ismail Haniya, and other members of the committee, al-Sinwar spoke of a bitter, brutal and unprecedented battle against Israeli forces being fought by the Qassam Brigades, the organization’s armed wing. He asserted that the Qassam Brigades had attacked at least 5,000 Israeli soldiers, killing a third, seriously injuring another third and permanently incapacitating another thir…