At least 48 people were killed in a blast which rocked a local market in Damboa district of Nigeria's northeastern state of Borno, a security source said.More than 40 people sustained various degrees of injuries by the blast which occurred on Tuesday afternoon at Sabon Gari community, the unnamed local security source told Xinhua.The bomb was planted inside the market. A deafening sound caused by the explosive device reverberated through the small community, the source added.A witness named Idrissa Saleh, who participated in the rescue operation after the blast, said the community was "devastated" by the incident as "most families in the small community lost a loved one".There has been no official statement on the attack.Last Sunday, suspected Boko Haram militants killed at least four people along Damboa road, not far from the market where the blast occurred.Boko Haram, the Islamist group, has killed thousands of people since its insurgency began in 2009.It has stepped up its campaign of violence since President Muhammadu Buhari took office late May, unleashing waves of attacks that have claimed more than 800 lives in just two months.