A United Nations official in Chad says attacks by Nigeria’s Islamic extremist group, Boko Haram on Lake Chad islands have displaced thousands of people.

World Food Program Chad director Mary-Ellen McGroarty told The Associated Press Tuesday that the agency in November assisted more than 60,000 fleeing insecurity. She said that it expects to assist 90,000 people in December.

McGroarty said the deteriorating security situation in the Lake Chad area has had a severe impact on communities.

A triple suicide attack on an island in Lake Chad Saturday killed at least 15 people, according to Chad’s government. Medecins Sans Frontieres and Chad security officials said more than 27 were killed.

The Lake Chad region straddles the borders of Chad, Cameroon, Niger and Nigeria.