A new Reporters Without Borders index cites hot spots in the Middle East, Africa and Asia as being among the worst offenders of press freedom. The journalism rights group also says there has been a significant decline in press freedom in the United States.

Reporters Without Borders says Syria has become an increasingly dangerous place for journalists during the nearly three-year conflict between the government and the opposition.

The group's U.S. director, Delphine Halgand, said Syria ranks near the bottom of the index of 180 countries. "You have to keep in mind that more than 130 news providers have been killed in Syria since the start of the conflict in March 2011, including 45 since last year. On top of that, at least 16 foreign reporters and 26 journalism providers are right now detained, kidnapped or missing," she said.

Elsewhere, Halgand said a "privatization of violence" is problematic in some African countries.

"What we mean is that non-state groups are the main source of violence against the media. This is the case in many countries in Africa like the M23 in the [DRC] Congo or the al-Shabab group in Somalia," said Halgand.

Reporters Without Borders looked at factors including transparency, media independence and level of abuses in its annual ranking of countries.

It says government attempts to crack down on social media sites and bloggers played a role in Vietnam's low index ranking of 174.

Viet Youth for Democracy co-founder Huong Nguyen said several of her friends who are bloggers have been jailed for using social media to express their views.

"The thing with social media is that it is so difficult for the government to control what people are talking about and for people to use and to discuss public affairs in the social media. That is why there has been a lot of focus from the Vietnamese government on restricting the freedom of information on the Internet," she said.

Reporters Without Borders says a government "hunt" for leaks and whistleblowers played a role in propelling the U.S. ranking down 13 positions to 46 on the index.

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Media Group: Press Freedom Slipping in Some Countries