US President Barack Obama has warned that Myanmar's reforms are by "no means complete or irreversible" after talks with democracy champion Aung San Suu Kyi at her Yangon home.

Speaking at a joint press conference on Friday, opposition leader Suu Kyi urged a "healthy balance between optimism and pessimism" towards the nation's stuttering reform process.

"They realise the difficulties that still lie ahead, but they must charge on," said Al Jazeera's Marga Ortigas, reporting from Yangon.

The talks marked a US show of support for Suu Kyi as Myanmar prepares for elections next year amid uncertainty about the direction of reforms.

Obama met with the opposition leader after arriving from the capital Naypyidaw, where he discussed the nation's troubled reform process with President Thein Sein.

We recognise change is hard and you do not always move in a straight line, but I'm optimistic.

Barack Obama, US President

"The democratic process in Myanmar is real," Obama said after speaking with the president late on Thursday. "We recognise change is hard and you do not always move in a straight line, but I'm optimistic."

However, the US leader also raised concerns over the direction of reforms, citing the cramping of freedom of expression, ongoing conflicts and the treatment of Myanmar's minority groups - especially the Muslim Rohingya.

Suu Kyi's National League for Democracy (NLD) party is widely expected to sweep polls in late 2015, but its figurehead is banned from the presidency by a constitutional clause.

Stalled reforms

On his last visit in 2012, Obama received a fanfare welcome from thrilled locals a year after Thein Sein began to open up the country.

Most political prisoners have been released and Suu Kyi has been elected as a lawmaker, while foreign investors have arrived in lockstep with the lifting of most sanctions.

But the atmosphere has slowly soured, with many observers saying reforms have stalled.

"So far they are being seen as too superficial," Ortigas said, noting the US has vowed it will provide greater support when the country implements broader reforms.

Suu Kyi cautioned against US "over-optimism" ahead of the visit by Obama, who has invested a large amount of political capital in Myanmar's transition from military rule.

His visit has coincided with the start of a debate on constitutional reform, in particular over the clauses effectively blocking a presidential bid by Suu Kyi and reserving 25 percent of seats for the military.

"I wondered when Obama first came, whether things will be better," 52-year-old street stall holder Minny Oo Aung told the AFP news agency in Yangon, where security is high, with clusters of police about every hundred metres. "But there has been no improvement in our society or economy."

Source: Al Jazeera and agencies