DHAKA: Bangladesh police have launched an investigation into apparent death threats against six secular writers, days after the murder of a fourth blogger in six months. The six, who include poets, bloggers and a journalist, all live in the southern city of Barisal and went to police after their photographs appeared late on Tuesday on a new Facebook page registered under the name Ansar-BD. "There are three anti-Islamic poets and three organisers of bloggers. They are the enemy of Islam. We should do whatever it takes," read the post. Police said they did not know who was behind the threat but were taking it seriously, and the country's elite security force was investigating. "We've increased surveillance and patrols near their homes and workplaces, "Barisal city's police chief said. The apparent hit-list was published less than a week after blogger Niloy Chakrabarti was hacked to death at his home in Dhaka by an unknown attacker. He was the fourth atheist blogger to have been killed since February when Bangladeshi-born US citizen Avijit Roy, a writer and moderator of a blog site, was hacked to death in Dhaka. The Bangladesh branch of Al Qaeda in the Indian Subcontinent, Ansar al Islam, claimed the murder of Chakrabarti and warned of more to come, according to monitoring group SITE.