At least 20 people were killed in an attack by Islamist terror group Boko Haram in Nigeria's Jingalta town, a security official said on Thursday.The attack took place on Wednesday when gunmen attacked several passenger vehicles in the town in Borno State, the official told Efe news.The official said the attackers not only opened fire at the vehicles, but also set them on fire.He noted that the terrorists were fleeing from an offensive launched by the Nigerian military in the area.