Nigeria's military and air force jets from allied countries attacked Boko Haram rebels in Gombe on Saturday.

After the attack, the Islamist fighters reportedly left in a convoy of vehicles filled with dozens of corpses of their comrades, according to an AP report.

"They were heard telling our people in the villages leading to Gombe that they have not come to harm civilians but the security agents. They were also dropping copies of papers with messages written in Hausa warning people not to participate in the coming elections, lest they risk being killed," said resident Malam Hassan.

A copy of the message in which Boko Haram warned that its fighters would attack polling stations in the March elections was obtained by AP.

The Boko Haram paper also said residents should not assist the army and pledged not to attack those who stayed out of its fight against the government.

"We are calling on you all to come and join us in the Jihad and embrace Islamic Sharia jurisprudence," said the leaflets from Boko Haram.

The fiercest fighting was about 3km (two miles) outside the town, resident Jummai Aliyu said.

The town of Gombe has been attacked many times, including a car bomb in December that killed around 20 people.

Overnight, Boko Haram carried out an attack on Chad, for the first time on Chadian soil, said officials.

Gunmen crossed Lake Chad in boats and attacked a village, an army spokesman told the BBC.

Chad recently joined Nigeria, Niger, and Cameroon in a military coalition against the jihadists who want to create an Islamic caliphate in Nigeria.

"They came on board three canoes and succeeded in killing about 10 people before being pushed back by the army," one resident told Reuters.

One Chadian soldier spoke to Sky News say the fighting was "very dangerous and hard".

"We don't even have time to sleep," he said.

"The fighting goes on through the night even."