DHAKA, Jan 31 (Reuters) - A policeman was killed and another injured in a bomb attack north of the Bangladesh capital, police said on Wednesday. "We don't immediately know who the attackers are. We are investigating the incident," said a police officer at Gazipur, 40 kms (25 miles) north of Dhaka, where the attack took place. Police have arrested at least 30 suspected Islamist militants and seized large quantities explosives across the country over the past two weeks. Five of seven top Islamists sentenced to be hanged for a spate of bomb attacks which killed dozens of people in Bangladesh in 2005 year have appealed to President Iajuddin Ahmed for mercy.They include Shayek Abdur Rahman, supreme leader of banned group Jamaat-ul-Muajahideen and Siddikul Islam Bangla Bhai, leader of outlawed Jagrata Muslim Janata Bangladesh.
