GENEVA – Two U.N. special experts, one on freedom of expression and the other on extrajudicial executions, are alarmed at the recent killing in Bangladesh of three secular bloggers writing against extremism in the name of religion.

"The recent killing of three bloggers in Bangladesh is an alarming signal of the deterioration of the space for freedom of expression in the country," the United Nations Special Rapporteurs on freedom of expression, David Kaye, and on extrajudicial executions, Christof Heyns, warned May 13.

The three journalists had strongly promoted free expression and were critical of fundamentalism of all kinds, they said.

They cited reports on Ananta Bijoy Das, who wrote for a website promoting "science, rationalism, secularism, freethinking, human rights, religious tolerance, and harmony amongst all people in the globe."

He was hacked to death in the city of Sylhet on May 12.

In February, the blogger Avijit Roy, A U.S. citizen who was killed and his wife seriously injured in a similar attack while in Dhaka. A month later, another blogger, Washiqur Rahman, was also killed in the Bangladeshi capital.

The UN Special Rapporteurs called for a prompt and thorough investigation of these cases.

They stressed that "it is vital to ensure the identification of those responsible for these horrendous crimes, as well as those who may have masterminded the attacks."

"These recurrent murders are reprehensible in and of themselves, and they exert a chilling effect with impact far beyond the direct victims," noted Kaye, an American law professor.

"Attacks against writers like Mr. Bijoy Das affect the society as a whole."

He noted, "Given the very public nature of these horrendous crimes targeting voices critical of extremism, it is very important that authorities publicly condemn the crimes and emphasize the importance of free speech online and offline."

Nations are under the obligations to provide, through judicial or other means, effective protection of individuals and groups who may be subject to extra-legal, arbitrary or summary executions, Heyns, a South African human rights law professor, noted.

The Special Rapporteurs urged the Bangladeshi authorities to consider specific initiatives to prevent the recurrence of attacks against writers and activists.

This should include not only the provision of particular physical protections to those who are potential targets for violence, but also open public debate challenging extremist views of all kinds.

Last week, Al Qaeda's affiliate in South Asia claimed responsibility for several killings of "blasphemers" in the region, including Roy and Haider, the Los Angeles Times reported.

A local militant group, Ansar al-Islam Bangladesh, said that Al Qaeda in the Indian Subcontinent had also claimed responsibility for the attack on Das, according to the SITE Intelligence Group, which monitors such groups online. But there was no immediate statement to that effect from Al Qaeda.