The press freedom watchdog Reporters Without Borders (RSF) says threats against journalists in eastern Sri Lanka have reached alarming levels.
In a report entitled "Terror Stalks Journalists in the East", the RSF says the situation is too volatile to say that press freedom exists in Sri Lanka.
The Tamil Tigers have meanwhile told Norwegian diplomats that the peace process is in great crisis.
They say that action is needed to deal with worsening security in the east.
In its report, RSF says it fears the current tensions may plunge the country back into war.
It says that would lead to new and serious violations of press freedom.
The Tigers say a proxy war is being waged against them
The report looks at the case of Aiyathurai Nadesan - the first journalist to be killed in Sri Lanka for three years.
It says colleagues and relatives suspect the killers were close to the breakaway rebel leader Colonel Karuna and had army protection.
It accuses the government of not enlisting sufficient resources to identify the killers and put them on trial.
The report makes suggestions to protect journalists in Sri Lanka.
The BBC Frances Harrison in Colombo says that foremost is fighting the culture of impunity - RSF says that in the last four years, those who murdered journalists or hired killers have never been brought to justice.
Among those are the killers of BBC reporter Nimalarajan Mylvaganam, who was killed in Jaffna in 2001.
RSF says there is no longer any doubt that the police are unable or unwilling to conduct investigations and gather evidence in this case.
The report complains that government harassment of the media has resumed with many Tamil journalists being treated differently from their Sinhala colleagues and some newspapers printing racial slurs.
Breakaway rebel Colonel Karuna is alleged to have the backing of the military
But it also criticises the Tamil Tiger rebels for instilling fear in Tamil journalists so they do not report rebel human rights violations.
Meanwhile, the Tigers say they have told Norwegian diplomats that the peace process is in great crisis.
They have urged the Sri Lankan government to deal with the deteriorating security situation in the east.
The head of the rebels' political office in Batticaloa died in hospital on Tuesday after being shot last week by unknown gunmen on a motorbike.
The Tigers accused the military of collusion in that shooting and another on the same day.
They say that rival Tamil groups aligned to the army have been fighting a proxy war against them in the east of the island - something the military denies.