U.N. humanitarian chief Valerie Amos is going to Mali, where a food crisis and unrest in the north have affected millions of people.

The United Nations says Amos will visit the capital of Bamako and the central town of Mopti during a three-day visit beginning Tuesday. Amos is to assess efforts to aid an estimated 4.6 million Malians affected by the food crisis and poor nutrition.

She is also to explore ways of improving access to northern Mali, where armed Islamist groups that control the region are trying to impose their strict version of Islamic law, Sharia.

U.N. officials have denounced the groups for alleged human-rights abuses.

One group, Ansar Dine, publicly executed a couple for alleged adultery. Another group, MUJAO, chopped off the hand of an alleged thief.

The radical groups seized control of the north soon after soldiers toppled the government in Bamako in late March.

The United Nations says fighting and insecurity in the north have driven more than 430,000 Malians from their homes, many to neighboring countries.

Both Bamako and Mopti remain under government control. The New York Times reported this month that hundreds of young militiamen are training in Mopti to fight the Islamists, but have almost no weapons.

Mali's interim government has vowed to retake the north, and West African bloc ECOWAS has offered to deploy a force of 3,000 to help drive out the militants.