A media watchdog's annual survey suggests that a zealous bid to protect national security has taken a toll on press freedom, above all in the United States.

The survey, released Wednesday by Reporters Without Borders, ranks the U.S. 46th among 180 countries, a fall of 13 places.

It also highlights the negative impact of armed conflict on media freedom. Syria, in a brutal civil war, ranked 177, just above Turkmenistan, North Korea and Eritrea. The Central African Republic, where a sectarian conflict has erupted, plunged 43 places.

Finland, the Netherlands and Norway continue to top the ranking.

Seven indicators are used to measure how the press is able to perform in each country, including the level of violence, pluralism of opinions, the legislative framework and infrastructure.