"These cowardly attacks are part of a pattern of violence against Afghan journalists, who display great courage every day as they practice a craft essential to democracy", Mr. Sopko said.
The killing of Shah is the second targeted killing of journalists in Afghanistan in as many weeks.
RSF named the others as: ToloNews cameraman Yar Mohammad Tokhi; three journalists for Radio Free Europe Ebadollah Hananzi, Sabvon Kakeker and Maharam Darani; two cameramen for Afghan network TV1, Ghazi Rasoli and Norozali Rajabi; and Salim Talash and Ali Salimi of local Mashal TV.
In a statement issued via its propaganda agency Amaq, it said the first bomber had hit the Kabul headquarters of Afghanistan's intelligence services and security forces, with a second blast targeting journalists who had rushed to the scene.
Among them was Shah Marai, AFP's chief Kabul photographer.
He assured that the government would spare no efforts to ensure the safety of journalists.
"We anticipated and are doing our best and have been successful at blocking many of these attacks on innocent people but unfortunately once in a while they get through because any terrorist organization that realizes it can't win by ballots and turns to bombs, this is simply what they do", Mattis said.
A separate shooting in eastern Khost province killed a reporter.
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And in a third attack, 11 children were killed in a suicide bombing meant to target North Atlantic Treaty Organisation troops in Kandahar province. He said the work of those journalists who died "helped lay the foundation for Afghanistan's thriving and resilient independent media".
"The bomber disguised himself as a journalist and detonated himself among the crowd", he said.
Marai joined AFP as a driver in 1996, the year the Taliban seized power, and began taking pictures on the side, covering stories including the United States invasion in 2001.
It comes days after the Taliban kicked off their spring offensive in an apparent rejection of calls for the militants to take up the Afghan government's offer of peace talks.
In 2002 he became a full-time photo stringer, rising through the ranks to become chief photographer in the bureau.
He was buried near his home village in the Shomali Plain, north of Kabul on Monday in a ceremony attended by heartbroken relatives, friends and colleagues.