The White House on Wednesday said that President Barack Obama called Myanmar's President HtinKyaw and de facto leader Aung San Suu Kyi, praising the move toward civilian-led government.
Obama called the pair to offer his congratulations, as military hardliners try to limit Suu Kyi's formal role.
Banned from becoming president by a junta-era constitution, Suu Kyi has cemented control over the country's first civilian-led government in decades by taking on a string of senior roles in the new administration.
She has vowed to rule "above" the president, picking school friend and close aide HtinKyaw for the role.
According to the White House "the president commended Daw Aung San Suu Kyi's determined efforts, over the course of many years and at great personal cost, to achieve a peaceful transfer of power and advance national reconciliation."