ISTANBUL, Turkey, March 26 (UPI) -- A bomb explosion at pro-Islamic State magazine Adimlar in Istanbul killed one writer and injured an editor Wednesday, Turkish police said.
The pressure bomb went off around 7:30 p.m. local time when a door opened at the magazine's headquarters.
Ünsal Zor, 45, a writer, was killed immediately and three others, including chief editor Ali Osman Zor, 47, and Cem Türkbiner, 30, and Cüneyt Karan, 39, were injured.
"The investigation into the incident is ongoing," a police statement read.
Adimlar is affiliated with Turkish Islamist group the Islamic Great East Raiders Front (IBDA-C) and has shown support for IS -- also identified by the acronyms ISIS and ISIL. IBDA-C is considered a terrorist group by the United States and European Union.
In October, Ali Osman Zor told CNN he supported IS' violence in reaction to what he called decades of Western imperialism in the Middle East.
"What about all the people killed by U.S. airstrikes? We haven't forgotten about Abu Ghraib," he said at the time, referencing the prison where U.S. soldiers were photographed abusing Iraqi prisoners.
Hurriyet Daily News reported a recently formed organization calling itself the People's Defense Unit claimed responsibility for the attack.
"Adımlar Magazine was punished for their justification of the massacres. Our actions will continue to the extent that such discourses continue. It is a crime to defend killers. No action will be left unpunished against revolutionists," the group said on its Twitter account.
But one staffer at Adimlar blamed the attack on foreign intelligence agencies.
"We know this to be the work of CIA and (Israeli intelligence agency) Mossad. We know this is an intelligence operation," the staffer said, speaking to CNN on condition of anonymity.
"There is nothing clear about the issue. I cannot confirm that this incident took place inside or outside the office. We can answer this question following the detailed technical investigations," Istanbul Gov. Vasip Sahin said.
The Turkish Press Council condemned the incident.
"It is not possible to accept the Adımlar Magazine bomb attack. It is against democratic principles and a crime against the humanity of media organs, founded for expressing ideas, to face such attack, no matter what their worldview is," a statement from the organization read.