A 13-year-old boy who was part of the group taken into custody at a squalid New Mexico compound last month has told FBI agents his mother's boyfriend was training him to conduct "jihad" against non-believers, according to federal court documents.

The boy was among 11 children and five adults living at the compound in Taos County when it was raided on 3 August by local sheriff's deputies who discovered a cache of firearms and the children living without food or clean water. The dead body of a three-year-old boy was found buried at the site later.

They initially faced state charges, then on Friday, the five adults including a Haitian woman described as the group's leader, 35-year-old Jany Leveille, were arrested by the Federal Bureau of Investigation and accused of conspiracy and firearms offences.

In an affidavit filed in support of a criminal complaint, an FBI special agent wrote that Ms Leveille's 13-year-old son told investigators that his mother's boyfriend, Siraj Ibn Wahhaj, 40, wanted to "get an army together" and train them for jihad.

The boy told agents that Mr Ibn Wahhaj trained him and another of Ms Leveille's teenage sons in firearms and military techniques, including rapid reloads and hand-to-hand combat, and told them jihad meant killing non-believers on behalf of Allah, according to the affidavit filed in US District Court in New Mexico.

New Mexico compound search Show all 6 1 /6 New Mexico compound search New Mexico compound search Aerial photo released by Taos County Sheriff's Office shows a rural compound during an unsuccessful search for a missing 3-year-old boy in Amalia, New Mexico AP New Mexico compound search Taos County Solid Waste Department Director Edward Martinez, center, surveys property conditions at a disheveled living compound at Amalia, N.M., on Tuesday, Aug. 7, 2018 AP New Mexico compound search Siraj Ibn Wahhaj, left, sits next to public defense attorney Aleks Kostich at a first appearance in New Mexico state district court in Taos, New Mexico, Wednesday, Aug. 8, 2018, on accusations of child abuse and abducting his son from the boy's mother AP New Mexico compound search Lucas Morton arrives in court to plead not guilty to child abuse charges in state district court in Taos, New Mexico, on Wednesday, Aug. 8, 2018 AP New Mexico compound search Subhannah Wahhaj appears in New Mexico state district court to plead not guilty to charges of child abuse in Taos, New Mexico, Wednesday, Aug. 8, 2018, alongside public defense attorney Greg Dawkins, left AP New Mexico compound search This Friday, Aug. 3, 2018, photo released by Taos County Sheriff's Office shows a rural compound during an unsuccessful search for a missing 3-year-old boy in Amalia, New Mexico AP

The 13-year-old also told the FBI that his mother believed she received messages from God, and that he watched her and Mr Ibn Wahhaj perform supposed "exorcism" rituals over the three-year-old boy, including one during which the boy choked and his heart stopped, according to the special agent's affidavit.

The teenager said his mother and others at the compound told him not to talk to anyone about the three-year-old ever being at the compound because they would "all go to jail."

Defence lawyers have said that the five adults were exercising their constitutional rights to practice their religion and own firearms, and that the group is being discriminated against because they are black and Muslim. The defence attorneys could not immediately be reached for comment on Saturday.

The five defendants came under FBI surveillance in May after Ms Leveille wrote a letter to Mr Ibn Wahhaj's brother asking him to join them and become a "martyr," state prosecutors have said.

They are due to appear in court in Albuquerque on Tuesday.