3 May 2013 Last updated at 12:05 ET

Media outlets and advocacy groups mark the 20th anniversary of World Press Freedom Day with complaints about what they see as a decline in the level of press freedom over the past year.

Some point to increasing dangers faced by journalists and new reporting restrictions, such as those recently introduced in Russia.

The proportion of the world's population living in societies with a fully free press has fallen to its lowest level in more than a decade, according to a report by the Washington-based advocacy group, Freedom House.

It says an overall downturn in global media freedom in 2012 was punctuated by a dramatic decline in Mali, a deterioration in Greece, and a further tightening of controls in Latin America.

Seven international broadcasters, including the BBC, meanwhile condemn challenges to what they describe as their "legitimate role" in offering free access to global media and coverage of events.

Alongside the blocking of internet services and cyber attacks, they highlight the deliberate jamming of both satellite and shortwave radio transmissions as part of a "concerted campaign of disruption" not seen since the end of the Cold War.

Some newspapers bemoan a disparity between constitutional rights and the actual restrictions they face. Hong Kong's South China Morning Post (SCMP) recalls an incident in January when a censor was alleged to have changed the headline and content of an editorial in the Southern Weekly newspaper without informing staff, prompting them to go on strike.

"Censorship is incompatible with progress towards a genuine advanced industrial economy," the SCMP says. "If China insists on holding back public debate, whether on web forums or in its press, it is likely that its phenomenal progress will stall."

Burma officially marked its first World Press Freedom Day after relaxing censorship and formally abolishing its censorship board earlier this the year.

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World's media lament decline in freedom