"There is no doubt it (their involvement in the attack)," she told a huge rally in front of the ruling Awami League's downtown central office here, marking the 10th anniversary of the attack which killed 24 people and injured over 200 others.
Hasina, 67, the president of Awami League, said the "terrorist attack" was aimed at eliminating the entire Awami League leadership. Her party today staged the public meeting at the scene of the attack coinciding with its 10th anniversary.
The attack is believed to be carried out by Islamist militants.
"The way Zia (Bangladesh Nationalist Party's founder and Zia's slain husband Ziaur Rahman) was involved in the August 15, 1975 carnage, identically Khaleda Zia and her son (Tarique Rahman) were involved in the August 21 (2004) attack there is no doubt about it," Hasina, who was the opposition leader during that time, said.
The August 15, 1975 coup killed Hasina's father and country's founder Bangabandhu Sheikh Mujibur Rahman along with most of his family members and toppled his post-independence government while Hasina and her younger sister Sheikh Rehana survived the putsch as they were on a visit abroad.
Senior army general Ziaur Rahman who subsequently emerged as the strongman of Bangladesh, had protected the killers under a now-scrapped indemnity law and rewarded them with diplomatic assignments abroad.
The Premier's comments came as prosecutors said they nearly concluded the trial with most of the crucial witnesses already testifying before the court which earlier declared Rahman a fugitive in the case.
Rahman is now staying in London and believed to have sought asylum in UK to evade justice while he is being tried in absentia. The British authorities have declined to reveal his immigration status citing their law.
Most other accused, including three former ministers of the past BNP-led four party alliance government, several Islamist militants and senior intelligence and police officers are facing the trial in person in a Dhaka court.
Hours ahead of the premier's public address, Zia's BNP called the August 21 attack a "horrible and act of terrorism".
The BNP claimed its innocence with a party spokesman saying "the Awami League blames us for political reasons".
"We want to equivocally say that BNP practices nationalist and democratic politics and there is no room for terrorism in our party. So, BNP has no link to the politics of killing and terrorism," BNP's top policymaking standing committee member Nazrul Islam Khan told the briefing.