Abdulrasheed Abubakar was paraded by police to make his statement
A member of the Nigerian Islamist sect behind a deadly uprising in July has confessed to receiving military training in Afghanistan, police say.
The member of the sect known locally as Boko Haram and Taliban said he was paid $500 to do the training and promised $35,000 (£22,000) on his return.
The uprising in northern Nigeria left some 700 people dead, mostly militants.
If confirmed it would be the first proven link between Islamists in the oil-rich country and Afghanistan.
Local people called the group Taliban because of its radical beliefs.
For years Western diplomats have feared an al-Qaeda sleeper cell might launch attacks on oil infrastructure in Nigeria, which is an increasingly large supplier to the US.
The man, 23-year-old Abdulrasheed Abubakar, was paraded before journalists in the Borno state capital Maiduguri, where the sect was based and which saw the worst violence.
The police also displayed a large cache of weapons and bomb-making equipment recovered from suspected Boko Haram members recently arrested in the northern cities of Yola and Maiduguri.
The BBC's Bilkisu Babangida said Mr Abubakar appeared confident and not at all nervous in front of the journalists.
He explained that he had converted to Islam seven months ago and decided to join the sect after buying the teachings of Boko Haram leader Mohammed Yusuf on cassette.
"It was the mood of Mohammed Yusuf's teaching - the energy that helped me to join him," he told the BBC.
He met Yusuf two weeks after finding the sect in Maiduguri and was asked by the Boko Haram leader to go to Afghanistan, he said.
He and one other person travelled to Afghanistan, taking two planes, he added.
"I spent three months in Afghanistan. I was trained as a bomb specialist."
Mr Abubakar said he was supposed to train five people on his return, but when he did not receive his money he escaped.
He said that during the uprising in July, when Boko Haram militants, armed mainly with machetes, launched the simultaneous attacks on police stations in different parts of the north, he was in jail in Yola.
After the uprising had been suppressed, many beheaded bodies were found in the sect's headquarters, including at least three Christian preachers and the second in command of the military operation.
Hundreds of sect members were also killed as the security forces retaliated and controversy surrounds the death of Yusuf, who was shot after his arrest.
Police say Yusuf was killed in a shoot-out when he tried to escape, but human rights groups say it was a summary execution.
The sect said it was fighting against Western education and believed Nigeria's government was being corrupted by Western ideas.
It wanted to see Islamic law imposed across the country.