ABUJA, Nigeria (AP) — The Islamic extremist group Boko Haram infiltrated the capital's main airport and was using a teenager to carrying out surveillance, Nigeria's intelligence agency said.

A 14-year-old boy was arrested at the Nnamdi Azikiwe international airport in Abuja earlier in the week, Tony Opuiyo, spokesman for the Department of State Services, said late Friday. The teenager said he spied on the movement of passengers and security and reported back to his handlers, said Opuiyo.

The intelligence agency said it's working closely with the Aviation Security Department and other groups to prevent any possible attacks at Nigeria's airports.

More than 1,000 people have been killed by Boko Haram violence since President Muhammadu Buhari was elected in March with a pledge to wipe out the extremists whose six-year-old uprising has killed an estimated 20,000 people. Doctors Without Borders said Friday that 75,000 refugees from Niger, Nigeria and Chad have been displaced from their homes in recent weeks due to attacks in the Lake Chad area.

Earlier this year, troops from Chad and Nigeria drove the extremists out of some 25 towns held for months in what had been declared an Islamic caliphate. The insurgents, who in March pledged allegiance to the Islamic State, have gone back to hit-and-run tactics and suicide bombings largely in the country's north.

Separately the Nigerian army said two soldiers were killed by land mines buried on highways by suspected Boko Haram extremists in Nigeria's Borno state. Two others were critically injured in the explosion as troops on a counterinsurgency operation engaged extremists in the Gudumbali area.

Umar reported from Bauchi state.