* Nigeria, Niger, Chad and Cameroon to mobilise units
* Combined force of 2,800 men due to tackle regional insecurity
NIAMEY, July 23 (Reuters) - Nigeria, Niger, Chad and Cameroon pledged on Wednesday to mobilize a joint force to tackle the growing regional threat posed by Boko Haram Islamist militants operating mainly in Nigeria.
Each nation is due to put forward 700 men to the force in the latest effort to improve the regional response to the militants, who have intensified the insurgency in northern Nigeria and carried out some attacks in neighbouring countries.
"This step is proof of our commitment to do everything possible to eradicate this curse," said Karidio Mahamadou, Niger's minister of defense.
The four countries, whose borders meet at Lake Chad, an area that is a Boko Haram stronghold, already share intelligence and coordinate border security in the zone, but mobilizing a regional force on this scale would be a major escalation.
The announcement was made after a meeting of the defense ministers from the four countries, but no details on the timing or location of the deployment were given.
The militants have killed thousands of people since 2009, when they launched their efforts to carve out an Islamic state in Nigeria.
Bombings and attacks have become common in Nigeria's north, but Boko Haram grabbed global attention some three months ago by seizing more than 200 girls from a school.
The kidnappings led to international calls for action and pledges from presidents in the region for a "total war" against the militants.
Niger and Cameroon have in particular bolstered security in the border areas but there have been no signs of a major offensive involving regional forces.
The militants have killed more than 2,000 civilians in the first half of this year, Human Rights Watch estimated a week ago.
At least 82 people were killed on Wednesday in two suicide bombings in the northern city of Kaduna, one aimed at an opposition leader and ex-president and another at a moderate Muslim cleric about to lead a crowd in prayer.
(Reporting by Abdoulaye Massalaki; Writing by David Lewis; Editing by Toni Reinhold)