Former finance minister and UN official Shah Abu Muhammad Shamsul Kibria, 73, was killed on Thursday in the blast at a rally of the main opposition Awami League party in Laskarpur, in the northeast of the country, where he was chief guest.
In protest, the Awami League has called for a three-day countrywide general strike from Saturday to Monday.
"We have decided to enforce a three-day non-stop strike across the country from tomorrow in protest against the latest bombing and grisly murder of Mr Kibria, one of the most senior and revered leaders of the party," former minister Obaidul Kader said after a party meeting on Friday.
Kibria's opposition colleagues blamed the government for failing to stop a string of bomb attacks that have killed and wounded dozens of people over the past year.
"If the previous blasts were properly investigated and the offenders were punished, today's incident would not have occurred," Tofayel Ahmad, a former commerce minister, told opposition supporters late on Thursday at the Dhaka hospital
where Kibria died of his wounds.
A fifth person died on Friday of wounds sustained in the blast, which police said was caused by a bomb or a grenade. Among the dead was a nephew of Kibria. About 70 people were wounded.
More than 70 were wounded in
the blast that killed Kibria
Prime Minister Begum Khaleda Zia called for an immediate investigation and arrest of his killers, and urged Bangladeshis to stay calm.
Opposition activists say bomb attacks are part of a conspiracy by the government to eliminate its opponents. The government rejects the accusations.
Awami party chief Shaikha Hasina said Kibria's death was an irreparable loss for the country and asked her followers to step up a campaign to force the government from power.
Political analysts say the violence and unending acrimony between the opposition and the ruling Bangladesh Nationalist Party could lead the country into anarchy ahead of parliamentary elections late next year.
"If the previous blasts were properly investigated and the offenders were punished today's blast would not have occurred"
Former commerce minister Toyfel Ahmad
Kibria joined the Awami League in the early 1990s after a career as a diplomat and an executive secretary of the UN cultural agency Unesco. He quickly became a prominent party policymaker.
Hasina narrowly escaped injury when grenades were thrown at a rally she was addressing in Dhaka in August. Twenty-three people were killed and hundreds were wounded in the attack.
The Awami League enforced a strike in Hobigaj, Kibria's home town, on Friday, where hundreds of activists marched through the streets, calling for the arrest and punishment of his killers.
In the capital Dhaka, angry opposition activists set fire to five vehicles and pelted stones at police.
Authorities called in extra police and paramilitary troops to reinforce security in several parts of the country on Friday.
The violence has raised concern about security for a meeting of leaders of the South Asian Association for Regional Cooperation in Dhaka on 6 and 7 February.