An Israeli air strike has killed the son of Hamas ’ chief negotiator in U.S.-mediated talks over Gaza’s future , a senior Hamas official said on Thursday, as leaders of the militant group held talks in Cairo aimed at safeguarding their truce with Israel. Azzam Al-Hayya, son of Khalil Al-Hayya, succumbed to his injuries on Thursday after being struck in an Israeli attack on Wednesday night, said senior Hamas official Basim Naim. He is the fourth son of Hamas’ exiled Gaza chief to have been