By Kieran Guilbert

DAKAR (Thomson Reuters Foundation) - The world must not forget about the impact of the Boko Haram insurgency on West Africa's Lake Chad region where 100,000 people are uprooted, as fears of famine rise in northeast Nigeria, aid agencies said on Thursday.

Nearly 250,000 children in Nigeria's northeast Borno state, where food is in short supply, suffer from life-threatening malnourishment and many are dying, the United Nations and Medecins Sans Frontieres (MSF) said last month.

Yet hunger and malnutrition rates across the border in Chad, where poverty and desertification have been compounded by Boko Haram violence, are troubling, said Pascal Nshimirimana, Chad program manager for the International Medical Corps (IMC).

"There is a lot of focus on the Nigerian side of the border, but the Chadian side is being forgotten," Nshimirimana said.

The region is the world's most neglected humanitarian crisis, the U.N. aid chief said earlier this year.

"Even before the Boko Haram crisis, the lake region and western part of Chad had been victimized by floods and drought," Nshimirimana told the Thomson Reuters Foundation by phone.

There are more than 100,000 people displaced by Boko Haram across the swamplands of Lake Chad, where the borders of Chad, Cameroon, Niger and Nigeria meet, the United Nations says.

Chadian troops have ventured onto Lake Chad, a Boko Haram stronghold, and say they are taking back ground from the Islamist group, undermining their seven-year campaign to carve out a Nigerian caliphate.

Yet there are still areas around the lake which are hard to reach and assist, the U.N World Food Programme (WFP) said.

"Insecurity, long distances, and a lack of infrastructure, with conditions made worse during the current rainy season, create additional hurdles to the provision of aid," said Abdou Dieng, WFP's regional director for West and Central Africa.

While the global acute malnutrition rate for the lake region stands at 13.5 percent, just below the emergency threshold, some areas north of the lake surpass it, at 18 percent, the IMC said.

Chad in April extended the state of emergency in the region, which has disrupted fishing, farming and cattle breeding and hit cross-border trade, markets and livelihoods, aid agencies say.

More than 15,000 people have been killed and at least 2.7 million displaced by Boko Haram across the four Lake Chad countries. Despite being driven back, the Islamist militants still stage raids and suicide bombings across the region.

"The effects of prolonged food insecurity are palpable in all four countries bearing the brunt of Boko Haram violence," Dieng of the WFP told the Thomson Reuters Foundation.

(Reporting By Kieran Guilbert, Editing by Katie Nguyen.; Please credit the Thomson Reuters Foundation, the charitable arm of Thomson Reuters, that covers humanitarian news, women's rights, trafficking, corruption and climate change. Visit news.trust.org)