Unidentified assailants have killed a newspaper editor in eastern Bangladesh, police said Tuesday.

Comilla Muktakantha editor Golam Mahfuz, 39, was killed early Monday in his combination residence-office in Comilla, a town 88 km  east of the capital, Dhaka, said intelligence official Mozammel Haque.

Police have detained four people for questioning but did not immediately have a clear idea about a motive, Haque said.

"We are trying to understand whether it happens for journalism or for any personal cause," he said.

Journalists in Bangladesh are often targeted for writing about corruption,

political violence or organized crime.

At least 10 journalists have been killed and dozens wounded in this country since 1997, media rights groups say.

Earlier this month, the New York-based Committee to Protect Journalists labeled Bangladesh one of the world's five "most murderous countries" toward journalists, along with the Philippines, Colombia, Iraq and Russia.

The Comilla Press Club released a statement formally protesting killing of Mahfuz, and announced a three-day mourning period.

More reports from Bangladesh