"President Obama did make some important statements and conveyed the message that he takes the human rights situation seriously. And he appropriately referred to progress as tentative," Suzanne Nossel, US executive director for Amnesty International, told AFP.
"The test will be is that pressure sustained? Obviously there are a number of different imperatives behind his trip."
The first US sitting president to visit the Southeast Asian nation, Obama also met Myanmar's reformist President Thein Sein and urged the former general to speed up the country's march out of decades of iron-fisted military rule.
"This remarkable journey has just begun, and has much further to go," he said in a speech at Yangon University. "The flickers of progress that we have seen must not be extinguished. They must be strengthened."
He also called for an end to sectarian unrest in the western state of Rakhine, saying there was "no excuse for violence against innocent people."
Two major outbreaks of violence since June between stateless Rohingya Muslims and ethnic Rakhine Buddhists in the state have left 180 people dead and more than 110,000 displaced.
Nossel said Obama "has got to continue to hold the regime's feet to the fire to fulfill their commitments."
Rights groups have voiced concern that the US rush to normalise ties with Myanmar, also known as Burma, is driven by economic ambitions to access a previously untapped market and could see human rights swept under the carpet.
"It's important that they don't now give the government of Myanmar just a free pass," she said, voicing concerns particularly about unrest in Rakhine.
"The elephant in the room that Obama needs to address is the role of the Burmese military in the country," wrote David Scott Mathieson, senior Asia researcher at Human Rights Watch on the group's website.
"The military remains the wild card in the reform process because it remains the country's dominant and dominating institution," he added, warning that "uncertainty" about its role was creating "great unease."
Obama must spell out the need for constitutional reform, he argued, also highlighting the criticism being leveled at democracy icon Aung San Suu Kyi for her refusal to condemn the plight of the Rohingya as well as the Kachin people.
Fierce fighting has raged since a 17-year ceasefire between the military and the Kachin Independence Army (KIA) shattered in June 2011, forcing tens of thousands of people to flee their homes in the far northern state.
Meanwhile, almost 70,000 people have signed a petition launched on Change.org by a Myanmar refugee, who left when she was a year old, and now lives in the United States.
Aisha Shanshudin had urged Obama to address the rights of the Rohingya people, saying "no human being deserves to (be) beaten, killed, or starved because of their ethnic and religious identity."
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