Nigeria's domestic intelligence agency has warned travelers to be ready for an attack on the capital's airport after announcing it had smashed a spy network run by the radical Islamist group Boko Haram.

The Department of State Services (DSS) said in a statement late Friday that it had arrested a 14-year-old at Nnamdi Azikiwe International Airport in Abuja who admitted he had been ordered to spy on security procedures.

Nigeria's military on Saturday repelled a Boko Haram attack on the key northeastern city of Maiduguri, a day after President Muhammadu Buhari took office vowing to crush the group, witnesses and security sources said.

The overnight attack on the Borno state capital saw rocket-propelled grenades fired into homes in a bombardment that reportedly lasted several hours.

Nigeria's military said on Tuesday said the country's sovereignty was not compromised despite the presence of Chadian ground troops in the northeast to fight Boko Haram.

Chadian soldiers crossed the border from northern Cameroon to the Nigerian town of Gamboru on Tuesday after three days of bombardment of Boko Haram positions in a regional fight-back against the Islamists.

A bombing blamed on Boko Haram in the heart of Nigeria's capital raised fears Thursday of a worsening Islamist insurgency, with the security forces struggling to prevent attacks in remote villages and near the seat of government.

Wednesday's blast, which killed at least 21 people, shook the crowded Emab Plaza in downtown Abuja during the afternoon rush as shoppers were buying groceries an hour ahead of the country's World Cup match against Argentina.

A loud explosion hit a crowded shopping center on Wednesday in Nigeria's capital Abuja, which has been repeatedly attacked by Boko Haram Islamists, the national rescue agency said.

"We received the information at about 4:00 pm (1500 GMT) about a blast" at the Emab Plaza, not far from the seat of government, said Manzo Ezekiel, spokesman for the National Emergency Management Agency (NEMA).

A car bombing at a bus station on the outskirts of Nigeria’s capital killed at least 18 people and injured 80, an official said Friday, just weeks after Boko Haram Islamists attacked the same spot.

The explosion rocked the crowded Nyanya bus terminal just a few kilometers from central Abuja at roughly 8:00 pm (1900 GMT) on Thursday, 50 meters from the site of an April 14 bombing that killed at least 75 people.

Nigeria police boosted security across Abuja on Tuesday after a bomb blast ripped through a packed bus station killing at least 72 people, the deadliest attack ever to hit the capital.

The slaughter on the outskirts of Abuja has raised fears that a deadly insurgency waged by Boko Haram Islamists may be spreading from the remote northeast areas the group has primarily targeted in recent months.

Nigeria's top human rights body on Monday said that eight people shot dead by intelligence agents in Abuja last year were civilians and not Boko Haram militants, as the government claimed.

The Directorate for State Services (DSS) said on September 20 last year that it uncovered an Islamist plot to attack a residential building used by federal lawmakers.

Two Lebanese suspects alleged to be members of Hizbullah and on trial in Nigeria on terrorism charges told a court Monday they were harshly interrogated by Israeli agents after their arrests.

Mustapha Fawaz, Abdallah Thahini and Talal Ahmad Roda were arrested in May after the discovery of an arms cache in a residence in the northern Nigerian city of Kano.

Nigerian prosecutors on Monday widened charges against three Lebanese nationals "accused of links to Hizbullah" as their trial began with access to the courtroom restricted and the identities of witnesses concealed.

Mustapha Fawaz, 49, Abdallah Thahini, 48, and Talal Ahmad Roda, 51, have been accused of having ties to Hizbullah and plotting attacks against Western and Israeli targets in Nigeria.