Cameroon says Chad will send a large contingent of troops to help it fight incursions from the Nigeria-based militant Islamist group, Boko Haram.

The announcement came a day after Chad said it would "actively support" its neighbour against the militants.

No detail was given about how many troops would be sent, or when.

On Tuesday, Cameroon said it had killed 143 Boko Haram militants who attacked one of its army bases at Kolofata near the Nigerian border.

It said one soldier had died during the assault, which led to a gun battle lasting five hours.

It was the first major attack on Cameroon since Boko Haram threatened the country's leader in a video posted online earlier this month.

The militant Islamist group has seized control of towns and villages in north-east Nigeria in a six-year insurgency.

President visits

A French-led initiative has called for Nigeria, Niger, Cameroon and Chad to contribute 700 troops each to a multinational force against Boko Haram, but no country has taken steps to implement the plan.

Niger and Cameroon have both criticised Nigeria for failing to do more to confront Boko Haram.

Chad previously had some troops based in Baga, a Nigerian town seized by Boko Haram earlier this month, but they had been withdrawn before the attack.

Correspondents say Nigerian politicians appear more focused on campaigning for elections next month than on security issues, and senior figures rarely comment on the insurgency in the north-east.

On Thursday, President Goodluck Jonathan made an unannounced visit to the area, his first for nearly two years.

He told displaced people in the biggest city of Borno state, Maiduguri, that he was "working very hard" to help them return to their homes.

Mr Jonathan's visit came as the human rights group Amnesty International released satellite images of towns attacked by Boko Haram, suggesting widespread destruction and a high death toll.

The pictures showed about 3,700 structures damaged or destroyed in Baga and neighbouring Doron Baga last week, the rights group said.

Amnesty's before-and-after satellite images were taken on 2 and 7 January.

Nigeria's government has disputed reports that as many as 2,000 people were killed in and around Baga, putting the number of dead at no more than 150.