The New York-based Committee to Protect Journalists (CPJ) pointed to a series of steps by the government of President Ali Abdullah Saleh to rein in the media, including the creation of a special court last year to prosecute press offences.

"Taken together, the government's long-standing practice of violent repression and its new legalistic tactics are creating the worst climate for press freedom since the country's unification in 1990," CPJ said in a report.

There was no immediate response from the authorities.

The group said criticizing Saleh, reporting on corruption among senior officials and on the government's campaign against southern secessionists and rebels in the north had become "red lines" for the press.

"The campaign continues today with an array of legislative proposals that would set prohibitive financial barriers for broadcast and online news outlets, expand the definition of criminal defamation to include virtually any form of criticism of the president, and increase prison terms," the report said.

After a Yemen-based arm of Al-Qaeda claimed responsibility for the botched bombing of a US-bound airliner in December, fears have grown that Yemen could unravel into a failed state allowing extremists to thrive and launch more attacks.

The impoverished Arabian Peninsula nation is trying to quell a resurgent regional arm of Al-Qaeda that has increased attacks on Western and regional targets, worrying the United States and other Western countries which have pledged political, security and financial support to veteran ruler Saleh.

At the same time, it is trying to cement a truce with rebels to end a civil war in the north that has raged on and off since 2004 and end a separatist rebellion in the south.

Opposition and rights groups in Yemen have made wide use of the Internet to criticize the government and report on opposition activity, including protests in south Yemen and a rebellion last year centered in the northern Saada province.

In January, a female journalist was sentenced to three months in prison for insulting the president and a writer was ordered to spend a year in jail for insulting Islam.

The United Nations Committee against Torture said last year that political activists, journalists and rights defenders had been arrested arbitrarily and held incommunicado during the fighting between the army and rebels in Saada.