The United Nations launched an appeal on Friday for $254 million to help hundreds of thousands caught in an Islamist insurgency aimed at carving out a caliphate in northern Mozambique. 

A group known locally as Al-Shabab unleashed a violent campaign in the gas-rich Cabo Delgado province in 2017 that has since killed more than 2,300 people and forced hundreds of thousands to flee. 

The UN said many people fled with just the clothes they were wearing and warned that 1.1 million people would need help next year. 

"They lost their belongings, their livelihoods, their future," said Myrta Kaulard, the UN's humanitarian coordinator in the country.

"Humanitarian assistance is vital to alleviate their suffering." 

The jihadists have launched hundreds of attacks since starting their campaign by killing two police officers in the port city of Mocimboa da Praia in 2017. 

The violence escalated this year and the militants now control swathes of the coast --including strategic ports and cities with gas installations -- and have advanced inland. 

"Women and girls are at risk of abduction, gender-based violence and exploitation, while boys are at risk of being killed or recruited by armed actors," said Kaulard, expressing particular concern about those trapped in isolated areas.

Thousands of refugees have poured into nearby towns and cities, staying with relatives or have been taken in by strangers, leaving local services stretched to breaking point, warned the UN. 

With the rainy season approaching, many areas hosting those fleeing the violence are expected to flood, ramping up the pressure to find a quick solution.