In related developments on Friday, the US Senate voted unanimously to urge the 10-member Association of Southeast Asian Nations (Asean) to suspend Myanmar until the military rulers there show respect for human rights.
The Senate resolution, approved concurrently by the House of Representatives, came days before the leaders of Asean meet in Singapore next week for their annual summit.
Earlier on the same day, a spokesman for the National League for Democracy, the party of Aung San Suu Kyi, the detained opposition leader, said in Myanmar that the generals had freed six political prisoners.
Said Nyan Win said those freed on Thursday included three party members and two other dissidents, Thet Naung Soe and Tun Lin Kyaw, who had staged solo protests in front of Yangon's City Hall.
The party said the authorities had freed more than 150 convicts from two prisons, but the others were common criminals.
One of the main purposes of Pinheiro's visit was to determine the number of people killed and detained in the September crackdown.
Pinheiro, a Brazilian academic, said that he would give as complete an accounting as possible only after drafting a formal report, and would present his findings to the UN Human Rights Council in Geneva on December 11.
"Until the generals' military hardware is crumbled, they won't listen to anyone"
Oomlwin, Yangon, Myanmar
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Myanmar's military government originally said 10 people were killed when troops opened fire on crowds of peaceful protesters on September 26-27.
Diplomats and dissidents, however, said the death toll was much higher.
Pinheiro said the authorities gave him post-mortem reports on 14 people whose bodies had been sent from Yangon General Hospital to be cremated.
He said that he would continue seeking relevant information from other sources.
Pinheiro said the government told him it had detained almost 3,000 people in connection with the crackdown, a figure previously announced.
The military says it has released most of them, but many prominent political activists remain in custody.
On Thursday, Pinheiro was allowed to meet several prominent political prisoners at Yangon's Insein Prison.
He described the facility, which holds about 10,000 prisoners, as being "old and overcrowded".
He also said the prisoners there needed medical treatment.
Pinheiro said he had one-on-one meetings with five political prisoners.
They included labour activist Su Su Nway, arrested on Tuesday as she tried to place a leaflet near a Yangon hotel where Pinheiro was staying; 77-year-old journalist Win Tin, held since 1989; and members of the 88 Generation Students group, who have been especially active in nonviolent anti-government protests in recent years.
Pinheiro expressed particular sympathy for Win Tin, a senior executive of Suu Kyi's party who is believed to be the country's longest-serving political prisoner.