Vijay Nambiar, the U.N. special envoy for Myanmar, said following a three-day visit to the country that the government needed to do more to address all segments of society and release all political prisoners.
"Only then can there be greater confidence that the efforts undertaken will indeed serve to meet the long-standing needs and aspirations of the people of Myanmar," he said in a statement. "There is no time to waste if Myanmar is to move forward."
Myanmar had its first general election in nearly 20 years in early November, saying it would open the door to civilian participation. The international community said the election was a sham, however.
Nobel Peace Prize laureate Aung San Suu Kyi led her opposition National League for Democracy to a victory in 1990 elections, though military authorities never recognized the results.
Suu Kyi was freed from house arrest last year in Myanmar, where she spent 15 of the past 21 years in detention, shortly after the November election.
Nambiar met with Suu Kyi but called on the government to take "concrete steps" to reform.