Washington's top Asia-Pacific official, Kurt Campbell, also said that a follow-up meeting to the one he held with the junta in November last year was on the cards.
"We have had some follow-on direct interactions with Burmese authorities, and I think we're going to be looking at a subsequent set of discussions in the near future," he told a news conference.
The US government last year announced a shift away from its policy of isolating the junta in favour of engagement, although it has maintained tough sanctions on the military generals.
Only if key demands are met, such as the release of opposition leader Aung San Suu Kyi and other political prisoners, and evidence that elections this year are free and fair, will the US consider lifting sanctions, secretary of state Hillary Clinton said.
Campbell did note some progress, such as the meeting last month between Suu Kyi and several National League for Democracy (NLD) party members, but added that ongoing persecution of ethnic groups by the junta would need to be addressed.
"We went into this ... with a very clear understanding of the challenges," Campbell told a news briefing. "But it is also the case that we're not unendingly patient. We will need some clear steps in due course."
The junta has announced that elections will take place this year, but has shown no signs of revising the 2008 constitution that appears set to entrench military rule.
Burmese political analyst Aung Naing Oo said that he was "not surprised" about the lack of clear progress in the country.
"You have two countries [US and Burma] that are diametrically opposed," he said. "One that thinks they are on a high moral ground and so demands progress, but I think that demand has shortcomings.
"You cannot expect results in a short time, and I think the US should be looking at longer-term developments. If the Americans really want democracy to return to Burma, they have to look at a five or 10-year [timeframe]."
He added that Thailand, for example, where many of Burma's political and economic refugees now reside, has been "experimenting with democracy for 80 years, and where are they now?"