At least 10 people have been killed and more than 20 injured by a 12-year-old female suicide bomber in Nigeria's Yobe state, media reported on Wednesday.The suicide blast took place on Tuesday at a market in the Gujba town of Yobe, the Nigerian Guardian reported."I saw the suicide bomber, a small girl of not more than 12 years," said Hussani Ibrahim, a driver at the scene. "She went into the market and headed straight to the grain section. She detonated her explosives in the middle of traders and customers," he recalled. The attack was consistent with the methods used by Boko Haram terrorist group, which has been stepping up suicide attacks after losing much of area in its control since the start of the year.In January, at least 19 people were killed by a female suicide bomber aged 10, in Maiduguri, the capital of Nigeria's Borno State.