The number of children forced to flee Boko Haram’s Islamic insurgency in Nigeria and neighbouring countries has reached 1.4 million, according to the UN children agency, Unicef.

Around 500,000 were displaced in the last five months after a sharp rise in attacks by the group, Unicef said.

Boko Haram has been waging a six-year insurrection to establish an Islamist state in the northeast of Nigeria that has killed thousands and displaced 2.1 million people, most of whom are children.

“In northern Nigeria alone, nearly 1.2 million children - over half of them under 5 years old - have been forced to flee their homes,” Unicef said in a statement, adding that an additional 265,000 children have also been uprooted in Cameroon, Chad and Niger.

Boko Haram controlled vast swathes of territory across three states in northeastern Nigeria at the beginning of 2015 but was pushed out by Nigerian troops with the help of Chad, Niger and Cameroon.

Now heavily splintered, Boko Haram factions have reverted to guerrilla tactics, raiding villages for supplies and bombing soft targets like places of worships, markets and bus stations.

Attacks spiked between the end of May and July, though the rainy season has seen a relative lull over the last month.

The largest concentration of internally displaced persons (IDPs), and therefore children, are in camps or host communities in the Borno state capital Maiduguri, the birthplace of the insurgency.

While the army has freed the last few towns still under some form of Boko Haram control, IDPs are reluctant to return home.