The US-based Committee to Protect Journalists has singled out leaders in Sierra Leone, Iran and China as being among what it calls the "ten worst enemies of the press".
In a statement timed to coincide with World Press Freedom Day, the committee says repressive regimes use measures ranging from torture to influencing judges in order to suppress the media.
Topping the annual list of offenders are Foday Sankoh, the leader of Sierra Leone 's Revolutionary United Front, Iran's Ayatollah Ali Khamenei and President Slobodan Milosevic of Yugoslavia.
Journalists killed
The committee says that last year, 34 journalists were killed doing their job.
Those it has labelled enemies of the press also include Malaysia, which, along with China, remains on the list of what are called repeat offenders.
China's President Jiang Zemin was named for the fourth year.
Malaysian Prime Minister Mahathir Mohamad was included for the second time.
An opposition newspaper in Kuala Lumpur, Harakah, is marking World Press Freedom Day by suing the government for restricting its publication, saying the limit on the number of editions it can print is politically motivated and unconstitutional.
The Committee to Protect Journalists is concerned at new reprisals against those who attempt to use new technology to provide what some rulers consider to be uncomfortable truths.
Controlling the internet
More and more governments are seeking to control the use of the internet.
However, in Australia the Press Council, which handles complaints about the media, has used the day to launch an information campaign encouraging the public to complain about reports on the internet, as well as traditional outlets.
Serious concerns about attacks on journalists have been echoed by the rights group Amnesty International.
It has called on governments to stop trying to control information by violating the human rights of those who work in the media.
It says reporters in Indonesia and other parts of the world have suffered torture, intimidation, assaults and bombings.