Abuja (AFP) - Nigeria's military on Thursday vowed to free more hostages from Boko Haram after nearly 500 were released from atrocious conditions this week in the group's Sambisa Forest stronghold.

Defence spokesman Chris Olukolade told reporters in Abuja the army would "comprehensively" clean out the forest, adding: "There is great hope for recovery of more hostages of the terrorists."

The army said on Thursday about 160 hostages were rescued from the dense, former colonial-era game reserve, while 200 girls and 93 women were freed on Tuesday.

The numbers underlined the scale of the tactic of mass abduction used by the militants, who according to Amnesty International have seized about 2,000 women and girls since the start of last year.

The human rights group's Africa director for research and advocacy, Netsanet Belay, said the rescues were a "cause for celebration" but he warned: "This is just the tip of the iceberg.

"There are thousands more women and girls, and men and boys, who have been abducted by Boko Haram," he said in a statement.





- 'Inhuman conditions' -





Female former hostages have described being subjected to forced labour, sexual and psychological abuse as well as having to fight on the frontline alongside the rebels.

The military released a series of photographs purporting to show some of the rescued women and children in an undisclosed location, huddled on the ground watched over by soldiers.

One very young child pictured appeared to be severely malnourished.

The rescue, after what the military said was a sustained aerial bombing campaign of the forest, raised hope that some of the 219 girls snatched from their school last year were among them.

Army spokesman Sani Usman has said the Chibok girls were not part of the group but defence headquarters in Abuja has said it was too early to say.

The mass kidnapping from Chibok, in Borno state, prompted global outrage and forced President Goodluck Jonathan to accept international help in the search operation for the missing girls.

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Olukolade said work was being undertaken to determine the former hostages' real identities but the priority was getting them to safety.

"Whoever they may be, the important thing is that Nigerians held captive under very severe and inhuman conditions have been freed by our gallant troops," he said.

Usman said earlier that the 160 or so hostages were rescued in an operation involving troops from the army's 7th Division, which has been tasked with fighting Boko Haram.

"We are still trying to compute the actual number of those rescued. But tentatively there are about 60 women of various ages and around 100 children," he told AFP.

One woman was killed in the fighting and eight other rescued hostages were injured. A soldier was also killed and four others wounded.

Several "terrorist training camps" were cleared during the operation while equipment and vehicles were seized, he added.

A military source indicated the women were used as human shields and in some cases fired back at soldiers until they were subdued.





- 'End the nightmare' -





Meanwhile, the United Nations special envoy for global education, Gordon Brown, said he would hold talks with Nigeria's president-elect Muhammadu Buhari on Thursday.

The former British prime minister said it was "time to end the nightmare" of kidnappings, which with forced conscription have been a regular feature of the bloody six-year insurgency.

"Now that some girls have been released we want all girls released," he said in a statement. "And we want them home with their families in days -- not months or years."

Brown has spearheaded an initiative to improve security at schools in Nigeria, which have been a target for the militants, who are opposed to Western-style, secular education.

Talks with Buhari, who won last month's elections, would focus on international military support to free the Chibok girls as well as improving access to secure schools for girls, he added.

Former military ruler Buhari has vowed to crush Boko Haram, whose quest for a hardline Islamic state in northeast Nigeria has left at least 15,000 dead and more than 1.5 million homeless since 2009.