Niger has imposed a state of emergency on the southeastern region of Diffa, where at least 40 people have been killed in recent weeks in attacks blamed on the Islamist militant group Boko Haram.

The government declared the 15-day state of emergency to help authorities increase security, impose a curfew, and restrict the movement of goods and people, according to an announcement on state television. It instituted similar measures in February.

Niger, Cameroon, and Chad have all suffered a spillover of violence from Boko Haram's northern Nigerian strongholds. Niger has arrested at least 1,100 suspected Boko Haram militants this year.

Diffa has endured at least 57 attacks since February, according to statistics published by the United Nations on Friday. At least 150,000 people seeking protection from Boko Haram attacks in Nigeria have taken refuge in Diffa, which lies along the northern shore of Lake Chad.

On Tuesday, UN High Commissioner for Refugees spokesperson Leo Dobbs said at a news briefing that Boko Haram's insurgency has effectively turned the swamplands of Lake Chad — where the borders of Chad, Cameroon, Niger, and Nigeria meet — into a "war zone."

"These people are living in desperate conditions, they lack livelihoods, they lack shelter, they lack food, they lack health care," he remarked.

Watch the VICE News documentary **The War Against Boko Haram:**

Boko Haram has waged violent attacks in Nigeria over the past six years, carrying out a campaign of bloodshed that has killed thousands of people and displaced more than a million others. While the Nigerian military has lately recovered territory from the group, Boko Haram has continued to carry out devastating suicide bomb attacks in the country's north.

As the group encroaches across the border into neighboring countries, Lake Chad's islands, surrounded by swamps, have made for a convenient base. About 60,000 people in the area have had to leave their homes. Many of them evacuated the islands out of fear of falling victim to attacks.