Fear of attacks by Boko Haram, the Islamist extremist group of northern Nigeria known for its deadly marauding and kidnappings, has uprooted a half-million children in the past five months, Unicef said in a report released Thursday.

The newly displaced bring the total number of children who have fled from Boko Haram militants in Nigeria and neighboring countries to 1.4 million, said the report by Unicef, the United Nations Children’s Fund.

The report’s findings suggested that efforts by Nigeria’s new president, Muhammadu Buhari, who was elected partly on a pledge to eradicate Boko Haram, were not going as well as he has asserted. Mr. Buhari said last week that military forces were gaining the advantage on Boko Haram, which has been waging a campaign of bombings, burnings, abductions and plundering for years through swaths of northern Nigeria, and more recently in Cameroon, Chad and Niger.

The group is perhaps best known for its abduction of more than 270 schoolgirls from the town of Chibok in Nigeria’s Borno State in April of last year.