Nnamdi Kanu, slotxo the leader of a separatist group that wants a breakaway state in eastern Nigeria, has been arrested.
His movement, the Indigenous People of Biafra (Ipob), has been labelled as a terrorist organisation by the Nigerian authorities.
He was initially held in 2015 on treason charges but then fled the country in 2017 while on bail.
Mr Kanu is a popular figure who has been a thorn in the side of Nigerian authorities since 2009.
He used his Radio Biafra station, which broadcasts from London, to call for an independent state for Igbo people.
Mr Kanu's arrest in 2015 triggered massive protests by his supporters in south-east Nigeria.
He was detained on Sunday with the help of Interpol, Nigeria's Attorney General Abubakar Malami said.
Mr Kanu was flown to Nigeria where he was presented in court on Tuesday by the country's secret police.
Mr Kanu founded Ipob in 2014 - the latest group advocating for a country for Nigeria's Igbos.
In 1967 Igbo leaders declared independence for the state of Biafra, but after a civil war, which led to the deaths of up to a million people, the secessionist rebellion was defeated.
But the idea of Biafra has never gone away and despite arrests of his members, Mr Kanu's movement has seen a recent swell in its numbers.