"They are misguided. They are enemies of Islam, democracy and the nation," Khaleda Zia, the Prime Minister, told her supporters on Wednesday at an anti-terrorism rally in the capital, Dhaka.
"We will crush them."
Bangladesh authorities deployed more than 6000 security forces for the rally, organised by the governing Bangladesh Nationalist Party, which attracted tens of thousands of people.
Earlier, the Bangladeshi government said it was planning a new anti-terrorism law after a spate of deadly bombings blamed on Islamic militants.
Moudud Ahmed, Law and Parliamentary Affairs Minister, speaking in an interview with private TV station ATN Bangla, said: "The existing laws are not enough to deal with this type of violence. We need a new anti-terrorism law,".
Ahmed said the new law would boost the maximum sentence from 10 years in prison to death for those convicted of involvement in terrorist acts.
Special tribunals would be set up for speedy trials, he said.
"What we are planning is a comprehensive law to tackle terrorism," Ahmed said.
He said the legislation would cover everyone from those who "encourage, motivate, provide training and money to those who are involved in the terrorist acts."
Bangladesh has been shaken by a string of bombings blamed on banned Islamic group Jumatul Mujahidin Bangladesh, which wants to replace the Muslim-majority Bangladesh's secular laws with Islamic rule.
At least 22 people have been killed and scores wounded in bombings across the country since the end of November.