It allowed a visit by U.N. Burma envoy Ibrahim Gambari at that time and is being pushed to admit him again quickly.
U.N. High Commissioner for Human Rights Louise Arbour told reporters in Ottawa, "We have to find out what has happened to these people who demonstrated. Where are they? How many -- credibly -- have been killed?"
"How many are still detained (and) under what conditions? So I really hope that collectively we'll be able to persuade the government of Burma to cooperate," she said.
Pinheiro said he planned to fly to Bangkok on Oct. 29 and visit Yangon by early November.
Burma's generals say 10 people were killed in September's crackdown. The protests were the biggest challenge to 45 years of unbroken military rule in the former Burma since 1988, when some 3,000 protesters were believed killed by soldiers.
"That number is quite low," Pinheiro said of last month's official death toll. "I am convinced that the number of the prisoners and the deaths are larger than the numbers estimated by the government," he said.
He said he has received conflicting reports on the number of people who were detained.
A 19-page report Pinheiro plans to present to the United Nations on Wednesday estimates Burma held nearly 1,200 political prisoners as of July 27, up from 1,100 in 2005.
Pinheiro cautioned that Burma's hand-picked commission announced last week to draft a new constitution could founder unless it includes Suu Kyi's National League for Democracy.
"If the commission is composed just of government people the problem will continue. How are you going to make a decision about democracy without the participation of the NLD?"
The military has run the country since 1962, refusing to hand over power even after the National League of Democracy overwhelmingly won a general election in 1990.
