Chad's president says fight against the insurgents is being hindered by failure of the two countries' troops to work together

ABUJA, May 11 (Reuters) - Chad's President Idriss Deby said on Monday in Nigeria's capital Abuja that the fight against Islamist Boko Haram insurgents was being hindered by failure of the two countries' troops to work together.

He said there were plans to form a rapid response force for the African Union from troops of the four countries around the Lake Chad basin - Nigeria, Chad, Niger and Cameroon.

Speaking to reporters after a meeting with Nigeria's outgoing President Goodluck Jonathan, Deby said he was disappointed that a joint agreement with Nigeria was not working. Chad has repeatedly complained about the lack of cooperation between the two armies since they launched offensives against the Islamist militant group earlier this year.

Deby also met president-elect Muhammadu Buhari, who beat Jonathan in the March 28 polls.

"It is regrettable that the two armies, that is the Nigerian army and the Chadian Army, are working separately in the field... If they were operating jointly, they would have achieved more results," President Deby said.

Having defeated al Qaeda in Mali two years ago, Chad's military believes it could finish off Boko Haram alone. It has notched up victories that have pushed the Nigerian militants back from the Cameroonian border.

The insurgents seized control of a swathe of northeast Nigeria last year, killing thousands in an unprecedented land grab while increasing incursions on neighbouring countries.

Nigeria has managed to roll back most of the group's gains since the start of the year with the help of offensives launched by Chad and Niger into Nigerian territory while Cameroon has repeatedly repelled attacks on its border towns.

Deby said that he did not know where Boko Haram's elusive leader Abubakar Shekau was hiding. Earlier this year, Deby threatened the militant chief by saying he knew where he was hiding.

"I cannot tell you today that I know where Shekau is hiding and even if I knew I wouldn't tell you," he said.

A statement from Buhari's press team said Deby and Buhari discussed Boko Haram's cross border activities and the impact on trade due to the destruction of key infrastructure, such as bridges, and how to work jointly to defeat the militants once the new administration comes into power.

"We know how Chad, Niger and Cameroon have been helping Nigeria to secure our border...we will sit and make sure we have a comprehensive review of the security situation in the northeast," Buhari said. (Reporting By Felix Onuah, Additional reporting and writing by Julia Payne; Editing by Hugh Lawson)

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