"Smoke from the home-made bombs and teargas shells covered the area, with people running for cover," one witness said.
The injured included 20 leaders of different parties, while police said they detained dozens of activists. About 230 people have been injured in clashes during the past three days.
"Why can't people in this country resolve their differences in a civilised way instead of resorting to violence and anarchy?"
Shafiq, Dhaka, Bangladesh
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Abdul Jalil, general-secretary of the Awami League, said they would defy all bans to implement their protest.
He called on alliance leaders and workers to resist the elections and urged voters to boycott the poll.
Reiterating an earlier ban, police said anyone causing disruption would be "dealt with severely" but they were braced for more violence as the alliance, led by Sheikh Hasina, the former prime minister, said it would block roads leading to the palace of Iajuddin Ahmed, the president, who heads the caretaker administration.
Hasina has accused Ahmed of bias and demanded that he and election commissioners step down before elections are held.