Burma's military authorities killed at least 31 people during the suppression of pro-democracy protests earlier this year, a UN human rights envoy has said.
The crackdown on the protests sparked an international outcry
Paulo Sergio Pinheiro said he gave Burma a list of 16 named individuals who were killed, in addition to 15 others confirmed as dead by the state.
Mr Pinheiro said the figures provided by the state after the unrest might "greatly underestimate the reality".
Earlier, Human Rights Watch released a detailed report on the crackdown.
The New York-based group said at least 20 people died when troops opened fire on protesters, but concluded that the total must be much higher.
Based on interviews with more than 100 witnesses, the HRW report described beatings, mass arbitrary arrests and torture of detainees.
It also said many more people were detained than the Burmese government had admitted.
Mr Pinheiro, who visited Burma last month, said more than 600 people were still being detained by the authorities and that a further 74 were listed as missing.
'Deaths in custody'
In a report due to be presented to the UN Human Rights Council next week, Mr Pinheiro said he had received information that the number of people killed during the anti-government protests was double the figure previously acknowledged by the Burmese authorities.
"Several reports of killings indicate that the figure provided by the authorities may greatly underestimate the reality," he said, according to extracts published by AFP.
"The use of lethal force by law enforcement officials from 26 to 29 September 2007 in Myanmar [Burma] was inconsistent with the fundamental principles reflected in the basic international norms deriving from international customary law," he added.
Mr Pinheiro was refused access to some detainees while in Burma
The UN special rapporteur said political and human rights activists had been targeted by the authorities and that those detained were subjected to cruel, inhuman and degrading treatment, and torture.
"Since the crackdown there have been an increasing number of reports of deaths in custody as well as beatings, ill-treatment, lack of food, water or medical treatment in overcrowded unsanitary detention facilities across the country," he added.
Mr Pinheiro said he received "credible reports" from a monk detained between 27 September and 5 October that at least 14 people, including eight monks and a boy, had died in custody due to the poor conditions.
He added that a large number of bodies wrapped in plastic bags and rice sacks had been cremated by state security personnel at the Ye Way crematorium in Rangoon on several nights at the end of September.
Mr Pinheiro said he had expressed his concern to the country's military leaders about the continued detentions and had urged them to return the remains of all the deceased to their families for burial.
On Monday, Burma's police chief said 2,927 people, including 596 monks, had been detained in connection with the pro-democracy protests, but that only 80 people, including 21 monks, remained in custody.
At least 3,000 people are believed to have died when the Burmese authorities brutally suppressed a popular uprising in 1988.