NAYPYITAW, Myanmar -- Confronting suspicion that his county's shift to democracy has gone awry, Myanmar's president appealed for patience Thursday from U.S. President Barack Obama and pledged to keep chipping away at concerns voiced by the free world.

Obama, his own global legacy at stake, held a firm line against alleged transgressions by Myanmar's government but offered a vote of confidence in Myanmar's commitment to reinventing itself after decades of military rule.

Despite pressing President Thein Sein on the government's treatment of Muslims and his slow walk on democratic reforms, Obama insisted he was still optimistic about the possibilities for the Southeast Asian nation's future.

"We recognize that change is hard and it doesn't always move in a straight line," Obama said. "In part because of President Thein Sein's leadership, the democratization process in Myanmar is real."

Obama was forced to confront the unsettling setbacks in Myanmar's transition to democracy by a pair of regional economic summits he attended this week in the country's sparkling new capital of Naypyitaw.

Two years ago, Obama paid a historic first visit to Myanmar, where he saw an opportunity to show U.S. engagement in Asia could be a force for good. He even lifted sanctions on the once-reclusive nation, but Obama returned to Myanmar this week with the country facing harsh scrutiny about whether its progress has petered out.

Thein Sein, who welcomed Obama in his opulent, sprawling presidential palace, said Myanmar had made solid progress toward alleviating the concerns of Obama and other world leaders.

"Some of the matters, we need time," Thein Sein said through his translator. "We definitely need to address all these concerns."

Obama's concerns were many, and he raised them both publicly and privately with Thein Sein -- himself a former member of the junta that ruled Myanmar for half a century.

A nationwide cease-fire with armed ethnic groups has yet to materialize. Myanmar's pro-democracy opposition figure, Nobel laureate Aung San Suu Kyi, is banned from next year's pivotal elections. Scores of Rohingya Muslims are fleeing for fear of violence at the hands of Buddhist mobs, while roughly 140,000 more remain in camps under dismal conditions.

Obama's meeting with Thein Sein focused largely on the persecution of the minority Rohingya and a need for constitutional reforms ahead of the election, said a senior Obama administration official. Obama used the word "Rohingya" multiple times, despite the fact that Myanmar officials bristle at the term.

Thein Sein, for his part, asked for more time to address the problems, the official said. And while Obama made no direct threats to reinstate sanctions, he did suggest that Myanmar stood to lose substantial U.S. business investment if it doesn't follow through on reform.

The U.S. official spoke only on condition of anonymity because the official was not authorized to comment publicly by name.

On Obama's way to the meeting, his limousine sped along an empty eight-lane highway before passing over a moat surrounding the large presidential palace, where beams of light cycled through red, blue and purple as they lit up a resplendent bay of fountains shooting water high into the air. Inside, gold carpet and furniture accentuated the white marble of the palace as Thein Sein greeted Obama and his delegation.

While in Myanmar, Obama announced the U.S. would start sending Peace Corps volunteers there in late 2015. The White House said the volunteers would train for three months to learn Myanmar's language, culture and technical needs, then serve at sites in Myanmar for two years.

Obama also met briefly Thursday with Aung San Suu Kyi, at a sparsely equipped building in Naypyitaw, a city whose very existence is an example of both Myanmar's aspirations for democracy and its challenges.

Carved from scrubland in the early 2000s, Naypyitaw has the lush hotels and impressive public buildings of a modern capital. But its vast empty spaces and eerie absence of people on the streets have led to a reputation as something of a ghost town.

At the Parliamentary Resource Center, a hub for aid organizations, Obama told Suu Kyi and her fellow parliamentarians he was heartened by their determination to move ahead with the transition. He said in some ways, the questions facing Myanmar echo those that Americans have faced, such as how to include minorities or prevent institutional discrimination.

"There are times when we'll offer constructive criticism about a lack of progress," Obama said. "But our consistent aim and goal will be to see that this transition is completed so that it delivers concrete benefits for the people."

Obama and Suu Kyi will hold more extensive talks Friday in Yangon at the lakeside house where the opposition leader was under house arrest for years.

White House officials said Myanmar's treatment of the minority Rohingya Muslims was high on Obama's agenda for his meetings. Another key U.S. concern is a need for constitutional reforms, such as the elimination of a rule that is keeping Suu Kyi off the ballot because her sons hold British citizenship.

In a sign of Obama's high regard for the opposition leader, when Obama called Thein Sein late last month to lay the groundwork for the visit, he placed a call the same day to Suu Kyi.

AP White House Correspondent Julie Pace in Naypyitaw contributed to this report.