Police unearthed what they called a mini ordnance factory
Security forces in Bangladesh have arrested the head of a UK-based charity who had been sought after weapons were found at a school it funded.
Officials said Dr Faisal Mostafa, who runs the Manchester-based Green Crescent, was arrested with a local aide on Monday.
Security officials raided the Islamic school, or madrassa, last month in the southern district of Bhola.
A large cache of weapons and bomb making equipment was found, police say.
The authorities presented Dr Mostafa, 45, at a press conference in Dhaka on Monday. He has not yet been charged with any offence.
Officials said he had been arrested in Gazipur, 40km (25 miles) north of Dhaka, on Monday, rejecting relatives' claims that he had been held for a number of days.
Dr Mostafa's father, Golam, had told Bangladesh's Daily Star he had been telephoned by relatives in Dhaka last Wednesday who told him that his son was in detention in the capital.
Dr Mostafa's whereabouts have been unclear since 24 March, two days after the raid on the madrassa.
Col Rezaur Rahman Khan of the Rapid Action Battalion told the AFP news agency: "Faisal and the local co-ordinator of the charity were arrested early Monday morning. They are suspected of using the Green Crescent-owned madrassa for militant training and making bombs."
Bangladeshi officials say that the madrassa is located on a remote river island only accessible via a drawbridge.
They have described the premises as a "mini-ordinance factory".
The BBC's Mark Dummett in Dhaka says the government fears that militant groups are rearming after two years of inactivity following the arrest and execution of their leaders.
The UK's Charity Commission has formally suspended Dr Mostafa as a trustee and will later consider permanent removal.
His family has said Dr Mostafa has done nothing wrong. The BBC contacted Green Crescent on Monday but there was no immediate response.
Newspaper reports in Britain say that Dr Mostafa has previously been tried and cleared of planning to cause terrorist acts by using high explosives.
In November 2008 Dr Mostafa was found guilty by a court in Manchester of possession of dangerous weapons and making a false statement about baggage cargo at the city's airport.