Suspected Islamic militants on Monday exploded several bombs at Bangladesh's three major railway stations, including one in the capital Dhaka, spreading panic among commuters and prompting authorities to step up security in the emergency-ruled country.

Security officials and witnesses said all the bombs exploded between 0645 hours and 0930 hours local time, rocking the railway stations in Dhaka's Kamalapur, north eastern Sylhet and Chittagong.

One person was injured in Chittagong, the southeastern port city, in the explosions.

Zadid al-Qaeda, an unknown outfit, claimed the responsibility leaving an aluminium plate at the explosion scenes with inscribes slamming the minority Kadiani sect of Muslims, also known as Ahmedias, and NGO activists, asking them to quit their jobs by May 10.

"Kadianis and NGO activists, be careful," it read.

Authorities ordered an immediate investigation while police and other security agencies launched a massive manhunt to find the suspected militants.

"It initially appeared that one single organisation exploded the bombs in a planned way," a security official said as the army troops, elite anti-crime Rapid Action Battalion examined the evidence at the scenes.

The blasts occurred a month after the execution of six top leaders of outlawed Jamaat-ul-Mujahideen Bangladesh, which had announced its presence carrying out a series of nationwide bomb blasts in Bangladesh on August 17, 2005.