"We're prepared for any kind of situation as there remains the possibility of further blasts," Inspector General of Police Abdul Kaiyum said on Saturday. He said security had been tightened across the country.
Police have been keeping a tight watch on key government buildings and installations and stopping suspicious vehicles since hundreds of virtually simultaneous blasts last month killed three people and injured more than 100.
Police said they found enough explosives and detonators to make 470 bombs during a raid late on Thursday on members of the outlawed Jamayetul Mujahidin group.
The authorities say they believe the group planted the 434 small bombs that exploded in nearly all the country's main towns and cities on 17 August. Some 30 bombs exploded in the capital, Dhaka.
Leaflets found at the blast sites bore Jamayetul Mujahidin's name and called for the introduction of strict Islamic law.
Bomb making equipment
In another raid on the house of Maolana Ataur Rahman, a brother of Jamayetul Mujahidin leader Shaikh Abdur Rahman, police said they found 700 electrical parts used to make time bombs as well guns and bomb-making manuals.
PM Zia labelled the attackers
'enemies of democracy'
"We have information Ataur Rahman, alias Sunny, was in charge of the 17 August blasts in Dhaka," said a spokesman for the Rapid Action Batallion (RAB), Bangladesh's elite crime-fighting force.
The RAB spokesman, who asked not to be named, said on Saturday a computer disk seized from Ataur Rahman's house contained the leaflet found at the blast sites as well as a bomb-making formula.
Police also said they found a large number of books calling for a jihad and military training CDs.
Kaiyum said police had arrested around 250 people over the blasts including six Jamayetul Mujahidin members during Thursday's raids.
Another man was detained on Saturday, police said.
Police are hunting for the Jamayetul Mujahidin leader and his brother as well as Siddiqul Islam, commonly known as Bangla Bhai, whose outlawed group Jagrata Muslim Janata is a sister organisation of Jamayetul Mujahidin.
Bangladesh's Islamist-allied coalition government said before the blasts the country had no Islamic extremist problem despite concern voiced by the opposition, neighbouring India and other foreign governments.
Later prime minister Khaleda Zia labelled the attackers "enemies of democracy" and said they had an "evil design" to destabilise the nation.