The radical Muslim cleric, Abu Bakar Ba'asyir, has been arrested on terror charges in Indonesia.Officials say he helped set up and fund an Islamic militant training camp in Aceh, uncovered by police in February.
The militant group - Jemaah Ansharut Tauhid - has been linked with alleged plans to kill Indonesia's president.
Mr Ba'asyir had previously served 26 months in jail before being cleared of involvement with Jemaah Islamiah (JI), the group behind the 2002 Bali attacks.
The 71-year-old was imprisoned for conspiracy over the bombings, in which 202 people died. However, his conviction was overturned and he was released in 2006.
He has been accused of giving spiritual leadership to JI, which has links to al-Qaeda - a claim he denies.
Mr Ba'asyir was arrested in West Java by anti-terror police but has not yet been formally charged. Under Indonesia's anti-terror laws police can question him for up to a week without filing charges.
Ansyaad Mbai, the head of Indonesia's anti-terror unit, told the BBC that Mr Ba'asyir was detained on terrorism charges.
"He had been involved in terror network in Aceh. As we know, that terror group in Aceh is linked with Jemaah Islamiah and many other extremist groups in our country," Mr Mbai told reporters.
"One of the allegations is that he provided funding to the Aceh military training camp. It's one of many allegations weighed against him," he said.
The BBC's Karishma Vaswani in Jakarta quoted police as saying that Mr Ba'asyir played an active role in setting up the camp, appointing key people and receiving reports from extremists in the field.
Our correspondent says these are very different allegations being levelled against Mr Ba'asyir, who has been linked to extremism in the past in a spiritual and moral capacity but not in the planning or creation of a terror network.
Arriving at Jakarta police headquarters, Mr Ba'asyir said: "This is God's grace to reduce sin. This is engineered by America."
Mr Ba'asyir's son, Abdul Rohim, appealed for the fair treatment of his father and said his mother had also been detained.
"We appeal to police to treat my parents well. He is innocent, he was just carrying out his obligations as a Muslim," his son said.
'New front in extremism'
Mr Ba'asyir is believed to be the leader of the hardline Islamist group Jemaah Ansharut Tauhid (JAT), which was created in 2008.
It was recently described in a report by the Brussels-based think tank, International Crisis Group as an "above-ground organisation" that embraced individuals with known ties to fugitive extremists.
Police raided JAT headquarters in Jakarta in May and arrested three of Mr Ba'asyir's followers.
They were charged with having links to the training camp in Aceh, the International Crisis Group said. Mr Ba'asyir denied having any links to the group or the camp.
Officials believe JAT had plans to launch an attack at independence day celebrations on 17 August, which are attended by the president.
The planned assault was said to be similar to that seen in Mumbai, India, in November 2008, when Islamist militants killed 166 people.
JAT has denied it has any connection to extremism and insists it is a legitimate Islamic organisation.
