U.S. President Barack Obama has voiced concerns about Cambodia's human rights record in what U.S. officials described as a "tense" meeting with Cambodian Prime Minister Hun Sen.
Obama, who arrived in the capital, Phnom Penh, Monday, raised the issue of free and fair elections and the detention of political prisoners.
U.S. Deputy National Security Adviser Ben Rhodes said Obama told the prime minister that those issues are an "impediment" to the United States and Cambodia developing a deeper relationship.
Cambodian officials said in response that the concerns over human rights were exaggerated.
After the talks with Hun Sen, the U.S. president met with the 10 leaders attending the the Association of Southeast Asian Nations - ASEAN summit in the capital.
Obama arrived in Phnom Penh, from Burma, where he addressed a crowd at the University of Rangoon earlier in the day. Obama said he had come to keep his promise and extend "the hand of friendship." He added that "flickers of progress" that have been seen must not be extinguished, but must become "a shining North Star" for all the nation's people.
The U.S. leader also touched on land seizures, and freedom to assemble and speak freely. He also called for an end of violence in Burma, citing the recent bloody ethnic clashes between Rakhine Buddhists and Muslim Rohingya.
Earlier in the day, Obama met separately with Burmese President Thein Sein and democracy icon Aung San Suu Kyi in the country's main city of Rangoon.
After an hour-long meeting, Obama, with President Thein Sein at his side, told reporters that the process of democratic and economic reform in the Southeast Asian nation can lead to incredible development opportunities. He added that he is looking forward to visiting again "sometime in the future."
The American leader met later with Aung San Suu Kyi, the nation's leading democracy activist, at her home in Rangoon. The two Nobel Peace laureates held a news conference after the meeting. Obama told reporters he has seen encouraging signs in the country in the past year, including Aung San Suu Kyi's release from house arrest and her election to parliament.
However, the Burmese democracy leader warned about the risk of what she called a "mirage of success."
"The most difficult time in any transition is when we think that success is in sight," she said. "Then we have to be very careful that we are not lured by a mirage of success, and that we are working to its genuine success for our people and for the friendship between our two countries."
President Obama has said his trip to Burma - the first by a sitting U.S. president - does not represent an endorsement of the government, but is rather an acknowledgement of the political reform process under way in the country.
After his meeting with President Thein Sein, Obama used the name "Myanmar" instead of Burma in his remarks to reporters. "Burma" is the name preferred by Aung San Suu Kyi and her democracy movement and it is the name that is officially used in Washington. Since 1989, the military authorities in Burma have promoted the name "Myanmar" as the conventional name for their state. The U.S. government did not adopt the name, which is a derivative of the Burmese short-form name Myanma Naingngandaw. Obama did not say why he used the term "Myanmar" Monday.
The trip underscores Obama's increased focus on Asia as he tries to fulfill his pledge to strengthen the U.S. economy during his second four-year term in office. The Obama administration has said American foreign policy and engagement will "pivot" toward Asia in the future.