A large amount of explosives has been seized and four people were arrested in Bangladesh's capital Dhaka and the southeastern port city of Chittagong, 242 km southeast of here, on Monday, police said.The Detective Branch (DB) of Bangladesh Police claimed to have seized 1,200 kg of explosive materials in Dhaka and Chittagong in separate operations on Monday, DB Joint Commissioner Monirul Islam told journalists.But he could not tell immediately whether the arrested persons were members of a militant group, according to Xinhua news agency.Bangladesh Police last week arrested 12 suspected militants, including the chief of the Al Qaeda in Indian Subcontinent, and recovered explosives and bomb-making materials from their possession.