Militant attacks that have forced hundreds of thousands of people to flee their homes in Mozambique's northern Cabo Delgado province have created a humanitarian crisis, the United Nations (UN) World Food Programme (WFP) said on Tuesday.

"What is happening is nothing short of a food security and nutritional crisis," WFP spokesperson Tomson Phiri told a UN briefing. "This is a humanitarian disaster."

The attacks have forced 570 000 people to flee, Mozambique President Filipe Nyusi said last month, saying he would defeat insurgents who stepped up attacks since pledging loyalty to Islamic State last year.

Speaking ahead of a joint briefing by UN agencies on Wednesday, Phiri said there were limited supplies so the cost of food had soared, while access to water and sanitation was also impacted, as was education.

The insurgent group, Ahlu Sunnah Wa-Jama, staged its first attack in 2017. Known at first mainly for beheadings, the fighters declared allegiance to Islamic State in June 2019 and since then have increased attacks in scale and frequency.