* Offensive against Islamists has not stemmed violence
* President Jonathan sacked military command after lapses
By Ibrahim Mshelizza
MAIDUGURI, Nigeria, Jan 24 (Reuters) - Nigerian Islamists killed 18 people and burned dozens of houses in attacks on two villages in remote northeastern Borno state, witnesses said on Friday, despite a military offensive aimed at stemming violence in vulnerable rural regions.
"Suddenly we heard gunshots in all directions and cries for help from women and children," said Wovi Pogu, nursing a gunshot wound from the attack on his village of Njaba in which 10 people were killed on Tuesday. Five others were wounded.
"As entered my house I was hit on leg and I fell down but I dragged myself to a nearby shack where I hid until the shooting subsided," he said, from his bed at a hospital in Borno's main city of Maiduguri.
Fighters from Boko Haram, whose campaign for a breakaway Islamic state has killed thousands in mostly Muslim northern Nigeria, also shot dead eight people in Kaya village before razing it to the ground on Wednesday, witnesses said.
Boko Haram, seen as the gravest security threat in Africa's top oil producer, torched two other villages on the same day, witnesses said, but no one was hurt. Colonel Muhammadu Dole, spokesman for Nigerian forces in the northeast, said he had no further details on the incidents.
A military offensive against the four-and-a-half-year-old insurgency that President Goodluck Jonathan ordered last May has pushed the rebels into remoter areas, but it has failed to stem the violence. It has also triggered reprisals on civilians.
Jonathan replaced his entire military command last week, after some embarrassing security lapses in rebel-affected areas, including an attack on the airport and military barracks in Maiduguri last month.
He also named Aliyu Mohammed Gusau, a northern Muslim, veteran army general and ex-national security adviser as a new minister in a cabinet reshuffle. Gusau is tipped to take the defence portfolio.
Jonathan, a southern Christian, has in the past been accused of giving too many key security posts to the largely Christian south, a charge he denied.