The Islamist Hezbollah militia in Lebanon vowed on Monday to quickly choose a successor to killed leader Hassan Nasrallah, and said it would continue its decades-long fight against Israel, even as it faced a massive escalation in military pressure. Deputy head Naim Kassem, in the first televised speech by a senior Hezbollah official since Nasrallah’s death, said the group would choose a successor to assume the secretary general position “as soon as possible.” Kassem said that the group’s structure allows it to find replacements for all senior members from among the ranks of deputies and other …