Myanmar released the results of its first nationwide census in 30 years on Friday but the survey excluded the country's Muslim Rohingya minority, who complain of deep state-sanctioned discrimination.
Most of Myanmar's 1.1 million Rohingya are stateless and live in apartheid-like conditions in the western state of Rakhine. Almost 140,000 were displaced in deadly clashes with majority Buddhists in Rakhine in 2012.
Delegates from southeast Asian countries were gathered in the Thai capital on Friday for talks on the "boat people" crisis. Thousands of migrants, many of them Rohingya, are adrift on boats abandoned by traffickers after a recent crackdown in Thailand. Myanmar said it could not be held responsible.
As the meeting was wrapping up, Myanmar's Ministry of Information announced its navy had intercepted a boat with 727 migrants aboard and was taking them to a base on an island off its southern coast to determine their identity.
The Myanmar government had promised international sponsors the Rohingya would be free to identify themselves as such in the census, conducted in March-April 2014, but backtracked a day before it started and said the use of the term would not be allowed.
"In northern Rakhine state, a considerable segment of the population was left out of the exercise amid ongoing communal tensions and the demand of many local people to self-identify as Rohingya, a demand not conceded by the authorities," said Vijay Nambiar, special adviser to the UN secretary general on Myanmar.
The count has also been criticszed for being based on a list of 135 ethnic groups which activists say is outdated and inaccurate.
The biggest surprise of preliminary results from the count released in August was data showing Myanmar's population stood at 51.4 million, some 9 million fewer than previous estimates. The full census broadly confirmed that, putting it at 51.5 million.
Both numbers include an estimate of the Rohingya population based on pre-census mapping in Rakhine state, UNFPA said.
The results of the census showed literacy among adults at almost 90%.
Data from other sources show deep poverty in the country.
Only a third of Myanmar's households have electric light, the infant mortality rate is 62 per 100,000 live births, and life expectancy stands at 66.8 years compared to neighbouring Thailand's 74 years, according to the World Bank.
Census data on ethnicity and religion, as well as figures on occupation and maternal mortality, will be released next year after the country's general election, scheduled for November.