Qader said: "Police have detained at least 1,500 activists alone in the capital, Dhaka, since Thursday. We'll enforce the blockade as per our plan."
However, Bangladesh's Daily Star newspaper quoted ABM. Bazlur Rahman, a Dhaka city police chief, as saying the clampdown was not related to any particular party or political allegiances.
Rahman said that police were holding those likely to create trouble and prevent a free and fair election and that "it is part of a continuous process".
Police said nearly 20 charred bodies were retrieved from the bus but many bodies were still inside the vehicle.
|Zia says she is not bothered |
by the poll boycott [AFP]
Despite arrests in Dhaka, about 5,000 alliance supporters rallied on Friday night in Dhaka to press their demands.
Abdul Jalil, a senior Hasina aide, said: "We are boycotting the vote because it will not be free and fair. We shall also not allow the holding of the polls."
The election commission has said the polls will go ahead as scheduled, regardless of the alliance boycott.
Hasina's alliance wants the ballot delayed until electoral reforms, including the revision of a voter list, are complete, and Iajuddin Ahmed, the country's president, has stepped down.
By boycotting the election, the alliance has left the contest largely to a four-party coalition led by Hasina's main rival, Khaleda Zia, the former prime minister and her Bangladesh National party.
Zia said on Friday: "We are not bothered by the boycott. We will take part in the polls."
A bus leaving Dhaka before the ensuing transport blockade, and following last week's Eid holidays, has killed at least 40 people.
The bus burst into flames near the eastern town of Comilla after a gas cylinder exploded.
|Sixty people were allegedly on the bus [AFP]|
Mohammed Kamal Uddin, a district police inspector, said: "A fire swept through the bus. We think only six people managed to escape the fire and the rest we fear were burned to death."
Survivor Jyotsna Akhter, 19, fled as flames swept through the bus within seconds of the explosion killing her mother, brother and sister.
"First there was a loud explosion and then I saw flames in the bus," she said, breaking down in tears.
"As soon as the bus caught fire, it turned over and all of a sudden there was fire everywhere. I was sitting at the front by the door so I jumped from my seat and got out."
Another witness said: "The bodies have been burnt beyond recognition."
A local police officer said: "Some 20 bodies have been removed from the bus so far. Survivors with burn injuries are being treated at local hospitals."