In its annual report, the New York-based Committee to Protect Journalists said that "a rise in censorship can be seen throughout Latin America, caused by government repression, judicial interference, and intimidation from criminal groups."
The report said governments abuse state resources to silence critical reporting and "powerful figures routinely use politicized courts to override constitutional guarantees of free expression."
It accused Venezuela's government of muzzling critics in the media, noting that allies of Chavez approved legislation allowing authorities to impose strict regulations on the Internet and tighten control over the broadcast media.
Chavez has "continued his aggressive campaign to silence critical news media," the report said.
The law approved by pro-Chavez lawmakers in December prohibits messages and images that "disrespect public authorities," ''incite or promote hatred" or crimes, or could create "anxiety in the citizenry or alter public order."
It also says electronic media must establish procedures to "allow the restricting, without delay" of content deemed objectionable.
Officials have not yet explained how the law will be enforced.
The media group also called attention to a Venezuelan court ruling that temporarily prohibited newspapers from publishing violent photographs.
"Relying on politicized courts, the government barred two major newspapers from publishing images of crime and violence in the run-up to September legislative elections," it said.
The committee's 2011 report also said violence linked to drug gangs is behind an increase in the killings of journalists in Mexico and Central America, striking fear into reporters and self-censorship within the media.
"Widespread self-censorship has been the devastating consequence of lethal violence by drug syndicates and criminal gangs," it said. "Dozens of killings and disappearances, bomb attacks, and multiple threats have led Mexican reporters and news outlets to abandon not only investigative reporting but basic coverage of crime."
The report said press freedoms have been limited by the courts in Brazil.
"Continuing a pattern of extensive censorship imposed from the bench, regional judges banned dozens of news outlets from covering some of the most important topics of the day, including issues involving the October general election, good governance, and public integrity," the report said.
It highlighted the court-ordered censorship imposed on the newspaper O Estado de S. Paulo and its website, banning them from publishing anything on alleged nepotism and corruption involving Fernando Sarney, son of former President Jose Sarney. The order was imposed in July 2009 when the daily - citing leaked wiretap transcripts from a federal investigation - said the Sarney family had used its influence to award jobs and give raises to friends and relatives.
The report did praise Brazil's government for "several successful investigations into journalist murders, representing a major step forward in the country's campaign against impunity."
But it said judicial censorship has become a grave problem, seriously inhibiting the ability of Brazilian journalists to report on issues of public interest. Reporters have been killed in the country's interior, where the state has a weak presence, while coverage of organized crime has exposed urban reporters to serious risks, the report said.
The committee condemned Ecuadorean President Rafael Correa for making regular use of a measure that forces the country's TV stations to broadcast rebuttals from government officials during programs that criticize Correa or his political allies.
Associated Press writer Stan Lehman in Sao Paulo, Brazil, contributed to this report.