"Chadian President Idriss Deby Itno has decided to send a substantial contingent of Chadian troops to back the Cameroonian armed forces who have faced repeated attacks from the Boko Haram terrorist sect with courage, determination and vigilance," the Cameroonian spokesman said in a statement.

The Cameroonian army says it killed 143 Boko Haram fighters who attacked a military base in the northern town of Kolofata on Monday, in what the government said was the militants' heaviest loss yet on its territory.

Thursday's announcement didn't specify how many Chadian troops would be involved or give a date for their deployment.

Chad's government on Wednesday pledged "active support" for  Cameroon in fighting Boko Haram. The offer followed a meeting in Chad's capital N'Djamena between President Idriss Deby and Cameroon Defence Minister Alain Mebe Ngo'o.

The Islamist Boko Maram group is fighting to create a hardline Islamic state in northeast Nigeria along the border with Chad, Cameroon and Niger.

Cameroon has been critical of the passivity of the Nigerian authorities and the international community in the face of Boko Haram aggression. Since Boko Haram's insurgency began, some 135,000 people have fled the restive northeast of Nigeria country and at least 850,000 have been displaced inside the region.

So far Chad has been spared, but only a narrow strip of land separate it from the Islamists' headquarters in the Nigerian state of Borno.

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