LAGOS (Reuters) - Nigeria’s state security agency said on Wednesday it had thwarted plans by Boko Haram militants linked to Islamic State to attack the British and United States embassies in the capital Abuja.

The Department of State Services (DSS) said a 20-year-old suspected Boko Haram member, arrested on March 22 in northeastern Yobe state, had confessed details of the plot.

Authorities arrested five more suspected Islamist militants in Benue state, in the country’s middle belt, and Abuja between March 25 and 26, the security agency said.

“The group had perfected plans to attack the UK and American embassies and other western interests in Abuja,” the DSS said in an emailed statement.

The agency described the suspects as “ISIS linked Boko Haram members” but gave no further details of how the militants planned to attack the embassies.

Boko Haram has killed more than 20,000 people and forced more than 2 million to flee their homes since 2009 in an insurgency aimed at creating an Islamic caliphate in the northeast of Africa’s most populous nation.

The jihadist group split last year, with one faction led by Abubakar Shekau operating from the Sambisa Forest - a vast woodland area in the northeast - and the other, allied to Islamic State and led by Abu Musab al-Barnawi, based in the Lake Chad region.

A U.S. Embassy spokesman declined to comment on the arrests. He said the U.S. mission “appreciates the work of DSS and Nigerian security forces in fighting terrorism and keeping citizens and residents safe”.

A spokeswoman for the British High Commission said: “We are in regular contact with the Nigerian security authorities concerning potential threats to UK interests in Nigeria.”

Boko Haram has largely focused its attacks on the northeast and neighboring Cameroon and Niger. Abuja has not been bombed since 2015. The most high profile attacks on the capital were in 2011 when militants bombed the U.N. headquarters, killing 23 people, and the police headquarters.

Separately, the United Nations Children’s Fund (UNICEF) on Wednesday said the use of children as suicide bombers by Boko Haram had surged in 2017. It said 27 children had been used in suicide attacks since the start of the year.