Clooney has been tasked with heading a new panel of legal experts who will advise the British government on how to encourage other countries to promote transparency and protect media workers.
"We are here because it's never been more dangerous to report the news," Clooney told a press conference on the sidelines of a G7 foreign ministers meeting in Dinard, northern France.
"According to the Committee for the Protection of Journalists, in the last five years, we've seen the highest number of journalists imprisoned since their records began over three decades ago," she added.
Clooney said her legal panel could propose reforms to repressive laws in countries and she raised the idea of sanctions that could be used on regimes "that have abused journalists."
Her experience defending journalists in countries such a Egypt and Myanmar "has shown me how easily vague laws and corrupt courts can be used to silence dissent and muzzle the media".
In December last year, Clooney blasted US President Donald Trump for giving a "green light" to regimes to persecute journalists through his anti-press rhetoric.
British Foreign Secretary Jeremy Hunt said on Friday that "democratic countries need to stand together to make it an international taboo of the highest order to order the arrest or detain journalists for doing their job".
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