Ibrahim Gambari made the comments Friday, at the end of a two-day visit to Cambodia.
Amnesty International says several people have been detained in Burma this month despite assurances from the military rulers the arrests would stop. Gambari says any further arrests violate "the spirit of national reconciliation" between the government and the opposition.
The U.N. envoy also says Aung San Suu Kyi should be freed from house detention if she is to play a part in the process.
Burma drew international outrage over its bloody crackdown of pro-democracy protesters in September. Fifteen people were killed and another 3,000 people detained.
Gambari is touring the Southeast Asia region to encourage Burma's neighbors to play a role in resolving the crisis.
His trip ended on the same day Burmese Prime Minister Thein Sein arrived in the Cambodian capital of Phnom Penh for talks with his Cambodian counterpart Hun Sen.
Cambodian Foreign Minister Hor Namhong says he told Gambari during a meeting Thursday that Phnom Penh supports Rangoon's efforts to improve the situation in the country, and says the regime should be given incentives instead of being slapped with sanctions. - VOA News