Almost 4,000 Chadians who have returned home from strife-torn Libya via Niger are in a critical situation in the border town of Zouarke, the International Organisation for Migration (IOM) warned on Friday.

"According to the Chadian government, more than 3,800 migrants including 310 women and children are in a very difficult situation in Zouarke with limited food, no water and transport to make their journey south," the IOM said in a statement.

Most of the migrants are Chadians, of whom 25,000 have already fled the Libyan conflict and made their way to the northern towns of Faya and Kalait, but the latest batch lacks the means.

"With no-one to help them and without transport to take them to Faya, 600 kilometres (370 miles) southeast of Zouarke, many are famished and suffering from exposure to extreme heat and dust. Water is also a key issue with the nearest well seven kilometres away from the town. Four people are reported to have died from drinking its contaminated water."

Heading for Faya, the migrants arrived in the border town between April 20-29 after making a long, dangerous journey from Libya via Niger, the IOM said.

"These are people who are really at the end of their tether..., who need immediate help," IOM spokesman Jean-Philippe Chauzy said, adding that Zouarke is in a mountainous region and hard to reach.