"It is an obligation of the whole world to help the Sahelian countries threatened by climate change, one of the causes of drought," said Jan Egeland after talks with President of Niger Mamadou Tandja on Thursday.

"I will talk with donors and international agencies, I will make a report to the Secretary General (Ban Ki-moon) on the problems that I have seen," he said on Niger's public television on Friday.

Egeland is on a four-nation African tour which has taken him to Mali, Burkina Faso in an bid to help draw attention of the international community to the problems of climate change and small arms proliferation in the Sahel.

Earlier in the week he told AFP from Mali that industrialised nations that caused climate change, have a moral responsibility to help the victims of the phenomenon.

He is to visit Lake Chad - once one of Africa's largest inland water body shared by Chad, Niger, Cameroon and Nigeria - to see the threats posed by the shrinking lake from which 22 million people depend on.

"The lake is dry on the Niger side, that causes a big problem for thousands of people including farmers, pastoralists and fishermen rendered extremely vulnerable," he said.

Persistent droughts and uncontrolled use of water have seen Lake Chad shrink in area from than 26,000 square kilometres (10,000 square miles) in the 1960s, to a current about 1,500 square kilometres.