Security forces were put on a state of high alert across Bangladesh on Tuesday after an apparently orchestrated bomb attack was carried out by suspected Islamic militants, officials said.
The blasts rocked the capital Dhaka and spread panic in two other cities leaving several people injured.
The attackers claimed that they were members of the new militant outfit Jadid al-Queda.
In hand written notes found at the sites of the explosions, the attackers threatened the Muslim minority Ahmadiyas and called on the people to quit jobs with Western-funded charities because of the latter's alleged anti-Islamism.
The explosions occurred at the main rail stations in Dhaka, the southern port of Chittagong and the northeastern city of Sylhet.
Police said the attacks were carried out within intervals of less than half an hour during the morning rush.
"The renewed attacks prove the presence of Islamic militants in the country despite the anti-terror campaign," said Inspector General of Police Nur Muhammed.
The latest militant offensive came a month after six Islamic extremists were hanged for their role in the murder of two judges more than a year ago.
Among those executed were Shaek Abdur Rahman and Bangla Bhai who had founded the banned militant body Jamiatul Mujahidden that carried out the first serial bomb attack in 2005.
Analysts said the rise of Islamic militancy could endanger the country's return to the democratic process.
Earlier reports said one person was critically injured in the serial blasts that spread panic among the train commuters.