Boko Haram militants are believed to be holding hundreds of captives in Nigeria's Sambisa forest, including more than 200 Chibok schoolgirls kidnapped in 2014.
The armed forces of Nigeria and Cameroon are trying to free the hostages, but the forest is a good place for militants to hide and a dangerous place for soldiers to operate.
The Sambisa forest reserve in northeastern Nigeria has been a key Boko Haram hideout for years.
Colonel Boubakar Bakary, one of Cameroon's senior military officers, commanding troops fighting Boko Haram around the forest, says Sambisa is very dangerous because it is one of Boko Haram's main remaining strongholds.
Many Cameroonian soldiers have lost their lives there. Many Cameroonian hostages they are looking for are in that forest. He says troops are doing everything possible to eliminate Boko Haram and take total control of the area.
Cameroon says 30 soldiers have been injured, and two killed, since a fresh offensive on Sambisa was launched in March. But Bakary said his troops have taken part in raids on the forest for more than a year.
Ideal hiding place
Part of the challenge is just how vast Sambisa is, covering parts of four Nigerian states. It's been called an ideal place for Boko Haram to hide because it's large, sparsely populated and has lots of tree cover that hampers aerial surveillance. It also has few roads and a rocky, hilly terrain, making access by land difficult to nearly impossible.
The Nigerian military has bombed the forest and succeeded in overrunning several Boko Haram camps, but the presence of kidnapped women and children remains a concern. Bakary says Boko Haram uses the captives as human shields. The forest, he said, is also infested with landmines.
Some good news
In the Cameroonian border town of Tourou, hundreds of people turned out Sunday to welcome home Habibba Assale.
Boko Haram grabbed the 16-year-old girl and several others two years ago and took them into Sambisa. She escaped last week during a raid by Nigerian soldiers but had to leave her baby behind.
She says after they were kidnapped, they spent a few weeks in a detention camp in a cave in Sambisa and then the girls were handed over to Boko Haram fighters as wives.
She says they were also given lessons on detonating bombs and told that if they died fighting Allah's course, they would go to paradise. She says she is very grateful to all the soldiers that saved her life but that so many girls and women are still in the forest.
"Obviously, beyond what popular opinion thinks, that you can just storm that place and then solve the problem, it is not that easy,” said Fonka Mutta, a Cameroonian journalist who accompanied the military into Sambisa this month.
Cameroon's military says it is giving food and medical care to liberated captives, but that it is impossible to know how many more Cameroonian citizens are being held. Families, fearing stigma and retribution from Boko Haram, don’t always report the abductions.