Officials in Bangladesh say several small bombs exploded at three railway stations earlier on Tuesday, injuring one person.
Police say the explosive devices, hidden in small bags, went off at stations in the capital, Dhaka, the northern city of Sylhet and southeastern port of Chittagong, causing panic among commuters.
Railway officials say thin metal sheets were found at two of the bomb sites. They were etched with messages warning people working for non-governmental agencies in Bangladesh to quit their jobs or be killed.
The messages also threatened a minority Islamic sect, Kadianis.
The messages were signed by a formerly unknown group that called itself Jadid al-Qaida (the new al-Qaida).
Police say an investigation is underway.
Matiur Rahman Choudhury has more on the story.