Troops have got another mandate to catch Boko Haram leader Abubakar Shekau alive.
Shekau is believed to have relocated from his bunker before the troops reclaimed Gwoza from the insurgents, a report has said.
The military is said to be probing the ?sudden disappearance of Shekau?, who has remained incommunicado.
According to PRNigeria, the search for Shekau followed the recovery of key towns and hideouts of Boko Haram.
The PRNigeria is the intelligence source through which the military and security agencies release strategic information.
The source said: ?With peace and quiet from the usually vociferous Abubakar Shekau, there are speculations within the security circles that the group may have been so disarrayed that it no longer has the luxury of issuing threats.
?A military source told PRNigeria that since the declaration of the final push against the insurgents in the middle of February, and directive to clear all terrorists? camps before May 29 handover date, Nigerian troops have been on the lookout for Shekau and other commanders of Boko Haram.
?The guy simply disappeared from the radar and suddenly vanished. We wish we can catch him alive.?
Another military source, who spoke in confidence, said: ?From intelligence report, Shekau has relocated from his bunker in Gwoza probably to Sambisa Forest or any other border town.
?Nobody, not even some of the arrested insurgents, could locate of get in touch with him now. This is why troops have been placed on red alert to arrest whoever is Shekau alive.
Troops yesterday retreated from Boko Haram?s last known stronghold ? the Sambisa Forest ? concerned the area was booby-trapped after three pro- vigilantes were killed by a landmine. A soldier is also believed to have been killed.
A vigilante and a security source both confirmed the pullback from the Sambisa forest, a day after an offensive aimed at rooting out the insurgents.
?The soldiers have retreated to Bama because of mines. They had been on the road but that made them vulnerable, so they moved to the bush but there are mines planted there (too),? one soldier, who did not want to be named, told Reuters.
The Sambisa forest, a former colonial game reserve, is about 100 km (60 miles) from the village of Chibok, from where Boko Haram abducted more than 200 secondary school girls a year ago.
Intelligence officials believed they were being held in the forest, but U.S. reconnaissance drones failed to locate them.
?Three of our boys were killed by a landmine as we progressed into Sambisa. We?ve suspended going farther,? Muhammad Mungonu, a member of a pro-government vigilante, told Reuters.
The militants controlled an area the size of Belgium at the start of the year, but have since lost much of that ground after a concerted push by militaries from Nigeria and neighbors Chad, Niger and Cameroon in the past two months.
Chadian military source said a joint military operation involving armies from Niger and Cameroon was expected to begin to encircle the Sambisa forest next week. Chadians will go in from the Cameroonian border where they have been massing troops.
?Boko Haram are in large numbers in Sambisa,? said the vigilante, who requested anonymity for security reasons as he was part of the operation.
?All their fighters who were pushed out of Bama, Dikwa, Gwoza and Damboa (in Borno state) all moved to Boko Haram camps in Sambisa,? he added.