By Lanre Ola MAIDUGURI, Nigeria, July 3 (Reuters) - Suspected Boko Haram insurgents attacked the outskirts of a state capital in northeastern Nigeria on Friday, escalating their attacks after a week of bloodletting in which more than 150 people were killed, military sources said. Heavy gunfire was heard coming from the fringes of Maiduguri, the capital of Bornoa state, for about half an hour on Friday evening.