By Waliur Rahman
BBC News, Dhaka
Police in Bangladesh say they have seized about 200 small bombs and arrested seven people in raids in the capital, Dhaka.
Two people were killed and more than 100 hurt last month
The raids follow last month's nationwide bomb attacks in which 400 devices exploded, killing two people and injuring more than 100.
Officers say they also found detonators, masks, weapons and CDs containing militant training manuals.
Police blamed last month's attacks on a banned radical Islamic group.
They believe the latest seizures are a major development in their investigation.
The raids were carried out late on Thursday night in two residential districts in Dhaka - East Bashabo and South Goran - by police and the elite anti-crime force, the Rapid Action Battalion (RAB).
One of the targets was an apartment rented by Ataur Rahman, the brother of the main suspect behind the serial explosions, Abdur Rahman.
Abdur Rahman is the chief of the banned Islamic group Jama'atul Mujahideen Bangladesh, which has been blamed by the government for the unprecedented attack.
Although no one has claimed responsibility for the bombings, leaflets found at bomb sites carried a call by the Jama'atul Mujahideen for the introduction of Islamic rule in Bangladesh.
Investigators now believe a banned leftist radical group, Janajuddha, or People's War, was also behind the attack.
Police say Ataur Rahman escaped his apartment before the raid.
Bangladesh's Prime Minister Khaleda Zia, in a speech to parliament on Thursday, vowed to tackle terrorism and proposed a new tougher law against bomb attacks.
Hundreds of people have been detained since the serial bombings.