The 12 militants were held in a crackdown as raids were conducted in different parts of the capital, Maksudul Alam, assistant director of Rapid Action Battalion (RAB) legal and media wing said.
Among the 12 arrested are -- Mufti Mainul Islam, Bangladesh's chief coordinator of Al-Qaeda in the Indian Subcontinent (AQIS), and his advisor Maolana Zafor Amin, he said.
"Huge stash of explosives, bomb-making materials, knives, training and jihadi books were seized from their possession," he was quoted as saying by the Daily Star.
AQIS had been planning an attack in the Muslim-majority nation after Eid-ul Fitr, Commander Mufti Mahmud Khan, the most senior RAB spokesman, told reporters.
"They've selected a madarsa in (the northern district of) Bogra for training," he said.
The group was financed by individuals from Saudi Arabia and United Arab Emirates, he added.
AQIS has claimed responsibility for the murder of secular bloggers Avijit Roy and Ananta Bijoy Das, who were brutally murdered this year.
AQIS is an al-Qaeda affiliate for militant activities in South Asia.
In September last year, al-Qaeda launched a new branch to "wage jihad" in South Asia to invigorate its waning Islamist extremist movement.
Al-Qaeda chief Ayman al-Zawahiri had said, in a video message, the new chapter would take their fight to Myanmar, Bangladesh and India.
