The one-time international pariah was formally awarded the rotating chair of the Association of Southeast Asian Nations (ASEAN) for 2014 at the end of the group's summit in the oil-rich sultanate of Brunei.

President Thein Sein said the theme of Myanmar's chairmanship would be "moving forward in unity in a peaceful and prosperous community".

The former general has earned international plaudits and the removal of most Western sanctions for reforms that include freeing hundreds of political prisoners.

Draconian media censorship has been scrapped and opposition leader Aung San Suu Kyi and her National League for Democracy have been welcomed into parliament following landmark by-elections last year.

But the military and its political allies remain firmly in control of the country while religious violence and the continued arrests of activists have tempered optimism about the political changes.

Addressing ASEAN leaders in Brunei, UN leader Ban Ki-moon hailed Myanmar's "unprecedented reform process".

"However, I remain concerned about ongoing communal violence," he added.

Around 250 people have been killed and more than 140,000 left homeless in several outbreaks of Buddhist-Muslim violence around the country since June 2012.

Critics said the decision to hand the reins to Myanmar highlighted the bloc's wider disregard for human rights.

"Sadly, respect for human rights has never been an important qualification for being ASEAN chair," said Phil Robertson, deputy Asia director at New York-based Human Rights Watch.

"Myanmar's human rights record is still highly problematic but this is nothing that ASEAN ever had a problem with," he told AFP.

"No one should forget that with a few exceptions, ASEAN continues to be a grouping of frequently dictatorial rights abusing states."

In April, Human Rights Watch accused Myanmar of "a campaign of ethnic cleansing" against members of the Rohingya Muslim minority -- an accusation rejected by Thein Sein as a "smear campaign".

Communal unrest last year in the western state of Rakhine left about 200 people dead and up to 140,000 displaced, mainly Rohingyas, who are denied citizenship by Myanmar.

Since violence broke out there last year, thousands of Rohingya -- including a growing number of women and children -- have fled the conflict in rickety boats, many heading for Malaysia.

For years Myanmar was a source of embarrassment for ASEAN's more democratic states, overshadowing other problem members such as communist Vietnam and Laos, which have significant human rights issues of their own.

In 2006, Myanmar was forced to renounce the ASEAN rotating presidency in the face of criticism over its human rights record and the then-ruling junta's failure to shift to democracy.

The Philippines -- one of the harshest critics within ASEAN of the former junta -- noted in Brunei that the Myanmar military had relinquished some of its powers.

President Benigno Aquino told Thein Sein that the Philippines would support Myanmar's chairmanship.

"I told him, 'Thank you that you listened (to world opinion and took the reform path). We will help in order to show you that your decision is right'," Aquino told reporters.

Along with the ASEAN chairmanship, Myanmar will host the East Asia Summit in 2014, which brings ASEAN members together with the United States, China and Russia, among others.

US Secretary of State John Kerry, speaking to students in Brunei on Wednesday, said Myanmar's reforms were not yet complete, a day after the country released dozens more political prisoners.

"I think what is happening in Myanmar is very exciting, but it is incomplete," Kerry said.

"Our hope is that the democracy will continue to evolve," Kerry added.

Relations between the US and Myanmar -- a traditional ally of China -- have improved markedly since the end of military rule with US President Barack Obama making a historic visit there last year.