Nigerian officials said on Saturday they had arrested the alleged leaders of a terrorist group accused of several high-profile attacks including a 2022 brazen jailbreak in the capital Abuja that temporarily freed hundreds of inmates.

Nigeria's National Security Adviser, Nuhu Ribadu, told journalists that Mahmud Muhammad Usman and Mahmud al-Nigeri had been captured during a "targeted operation" between May and July.

He said they were the leaders of Ansaru terrorist group.

President Bola Tinubu's spokesman Bayo Onanuga described the capture in a social media post as a "significant breakthrough in the war against terrorism."

'Have been on most-wanted list for years'

The group was also accused of blowing up rail tracks and raiding a train travelling from the capital Abuja to the northwestern city of Kaduna also in 2022. Eight people were killed and dozens more kidnapped and held for months.

They "have been on Nigeria's most-wanted list for years" and were also on international wanted lists, Ribadu said.

"They jointly spearheaded multiple attacks on civilians, security forces, and critical infrastructure," he added.

In July 2022, insurgents used guns and explosives to blast their way into a prison on the outskirts of Abuja, freeing dozens of inmates. Ansaru subsequently claimed responsibility.

Classified as terrorist organisation

The arrests mark a breakthrough in the West African nation's decade-and-half long battle against insurgents in the northeast – and, more recently, against criminal gangs behind kidnappings for ransom in central and northwestern regions.

Ribadu said the two had been involved in several high-profile kidnappings in the regions.

The Boko Haram splinter group was formed in 2012, later aligning itself with Al-Qaeda.

The United States in 2013 designated the group alongside Boko Haram as "Foreign Terrorist Organizations".

'Significant achievement'

Ribadu said the capture of the group's leader and deputy commander, "marks one of the most significant achievements to date in our ongoing effort to rid Nigeria of the threat of terrorism."

Ansaru broke away from Boko Haram in 2012, setting up its base in Kano.

The United States said the group kidnapped and executed seven international construction workers in 2013.

According to Ribadu, Usman and al-Nigeri masterminded several high-profile kidnappings and armed robberies, using the proceeds to "finance terrorism over the years."

Prison raids, kidnaps, and killings

Several hundred inmates were freed before being recaptured by security forces in July 2022 when Ansaru attacked the Kuje medium-security prison just 40 kilometres away from the capital and the Aso Rock presidential villa.

In 2012, the group raided a police station in the capital city, killed police officers and freed detainees from prison.

The group was responsible for the 2013 kidnap of a Briton and an Italian in Kebbi state. The duo were killed in a botched rescue operation by British and Nigerian forces.

The group also claimed responsibility for the kidnap of a French engineer in northern Katsina state in 2012. He later escaped.