Naypyitaw, Myanmar (BBN)-US President Barack Obama is to hold talks with Myanmar's President Thein Sein, hours after accusing his government of backsliding on reforms.
Obama is in Naypyitaw for the East Asia summit, which follows Wednesday's Asean meeting, reports BBC.
In an interview with a Thai-based Burmese website ahead of his arrival, he said that progress had been made.
But he said reform momentum had slowed in Myanmar and that there had even been some steps backwards.
"Burma is still at the beginning of a long and hard journey of renewal and reconciliation," Obama wrote in the interview with The Irrawaddy magazine.
In some areas there had been progress, he said, including "the release of additional political prisoners, a process of constitutional reform, and ceasefire agreements" relating to conflicts with Myanmar's minority groups.
But he said progress had not come as fast as many had hoped when the transition from military to civilian rule began in November 2010.
He cited restrictions on political prisoners, the arrest of journalists and the ongoing plight of the Rohingya Muslim minority displaced in Rakhine state after anti-Muslim violence.
"Even as there has been some progress on the political and economic fronts, in other areas there has been a slowdown and backsliding in reforms," he wrote.
So did the reformers run out of steam? Did Thein Sein's project reach a roadblock manned by hardliners in the Burmese army? Or perhaps we're close to the final destination - that is, with sanctions lifted and the army still really in charge.
Suu Kyi's main frustration is that the constitution remains unchanged.
Drafted in 2008, it entrenches the military's control of political life, guaranteeing it a quarter of the seats in the Hluttaw (the Burmese parliament), and a veto over any changes to the constitution.
This is what its architects proudly call a "disciplined democracy".
Has Myanmar's reform journey ground to a halt?
The is Obama's second visit to Myanmar. He last came in November 2012, in what was the first visit to the nation by a US president.
That visit came two years after the country embarked on political reform, following elections in November 2010 that replaced military rule with the military-backed civilian government of Thein Sein.
Many political prisoners were released, media restrictions eased and pro-democracy leader Aung San Suu Kyi released from years of house arrest.
Amid the reforms, her National League for Democracy rejoined the political process and secured a small block of seats in parliament after a landslide win in by-elections in 2012.
But Suu Kyi has recently warned that reforms have stalled, as all eyes turn to 2015 when the next general election will be held.
Obama meets Suu Kyi - who is currently banned by a constitutional clause from the nation's presidency - in Yangon on Friday.
"I'm especially interested in hearing her thoughts about the constitutional reform process, next year's election and how the international community, including the United States, can help ensure that the vote is inclusive, transparent, and credible," Obama wrote.
Obama's meeting with Thein Sein will take place on the sidelines of the East Asia summit - which groups the Asean bloc with the US, China, India, Japan, South Korea, Australia, Russia and New Zealand.
On Wednesday Asean (the Association of South East Asian Nations) held its own meeting in the Burmese capital.
Key issues included tensions over ongoing territorial disputes in the South China Sea and efforts to prevent fighters from Asean nations travelling to the Middle East to join extremist groups.
BBN/JF-13Nov14-11:30am (BST)