Hasan Shahriar Dipu and Shafaet Wahid, both aged between 20 and 25 and students of computer science, who live in New Elephant Road area of the city, admitted to have sent the email from Dipu's computer 'just for fun'.

The email addressed to the prime minister, with a copy to the inspector general of police, asked a Tk 3-crore ransom for sparing their lives.

It was not confirmed whether the PM opened the mail or not.

"Intelligence agencies went into investigation and tracked down the source of the email received by the IGP," police said.

Dipu was arrested in his house in the evening and Wahid near Mina Bazar on charge of the cyber-terrorism, sources said.

Police also confiscated Dipu's personal computer from his house and confirmed that the same machine was used to email the threats.