"The truth is that freedom of the press, whether symbolized by a pencil, a pen, a camera, or a microphone is under siege, purposefully," Kerry told a conference called to examine ways to improve security for journalists.
"That is because some people, some groups, and even some governments want to dictate the truth, want to define it, want to hide what we would know to be the truth."
"Obviously, we cannot and we will not let that happen," he vowed after the "outrage" in Paris earlier this month when Islamist attacks on the offices of Charlie Hebdo and on a Jewish supermarket left 16 people dead.
He recalled that in 2014 at least 60 journalists were killed and 73 in the preceding 12 months -- paying tribute in particular to Americans James Foley, Luke Somers and Steven Sotloff, who were murdered by militants from the Islamic State group.
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"In the past, it was extremely rare for a member of the press to be intentionally targeted, stalked, followed," he said.
"But in our era, roughly two-thirds of the reporters who die violently are killed because of, not despite, their profession."
The focus of the conference hosted at the State Department was how better to protect journalists working in dangerous environments.
Kerry said a particular focus was on local reporters and freelancers, who often lacked training and support.