Leaders from the South East Asian body Asean have called on fellow member Burma to release political prisoners and begin moves towards democracy.
Burma's Aung San Suu Kyi remains under house arrest
Correspondents say the unusually direct wording showed Asean's members were no longer hiding frustration at Burma.
The statement came as Amnesty International reported little sign of improvement in Burma's rights record.
Asean leaders will be joined by six other regional leaders on Wednesday, for the inaugural East Asian Summit.
"We took note of the briefing by [Burmese Prime Minister Soe Win] on the latest developments in the implementation of its roadmap to democracy. We encouraged Myanmar to expedite the process," the statement from 10-nation Association of South East Asian Nations said.
"We also call for the release of those placed under detention."
AUNG SAN SUU KYI
1990: National League for Democracy (NLD) wins general election while Suu Kyi under house arrest; military does not recognise the result
1991: Wins Nobel Peace Prize
1995: Released from house arrest, but movements restricted
2000-02: Second period of house arrest
May 2003: Detained after clash between NLD and government forces
Sep 2003 Allowed home after operation, but under effective house arrest
A new report by Amnesty International released on Monday said it knew of 60 new political detainees who had been seized or jailed in Burma during 2005.
It added that though some 260 were released by the country's military regime in July, the overall picture was little improved - more than 1,100 political detainees remain in jail.
Break with history
Concerns about Burma's political situation - those political detainees include pro-democracy leader Aung San Suu Kyi, whose house arrest was extended last month - was also at the heart of an agreement that Asean start work on a charter promoting democracy, human rights and good governance.
"The charter would govern everyone but the Myanmar issue was the trigger," a South East Asian official told the French news agency AFP.
The response to concerns over Burma is unusual because Asean has a tradition of keeping out of the internal affairs of its member states.
But it is under strong international pressure to take a harder stand on the lack of democratic reform in Burma.
The group welcomed Burma's invitation to Malaysian Foreign Minister Syed Hamid Albar, as a representative of Asean, to visit the country and "learn firsthand of the progress" in the democratic process.
Burma is not the only issue which threatens to overshadow the conference.
There is an ongoing row between Japan, China and South Korea over Tokyo's attitude to its wartime history.
And South Korea's trade minister has expressed disappointment that Thailand has not joined its Asean colleagues in signing a trade agreement with Seoul, due to South Korea's insistence that rice remains on a list of protected products.
Inter-regional trade will also be on the agenda when Asean's 10 member states join with premiers from India, China, Japan, South Korea, Australia and New Zealand for the inaugural East Asia summit.