The Burmese government was surprised by the scale of arch-rival Aung San Suu Kyi’s win in parliamentary elections, the president’s chief adviser acknowledged Monday, one day after the democracy advocate’s party apparently secured a resounding victory.

Suu Kyi’s party said it had won 43 of 45 contested seats in the landmark election. The results, said reformist President Thein Sein’s chief adviser, proved that this Southeast Asian nation is capable of holding fair elections and that it is time for the U.S. government to lift sanctions on Burma.

“I think the Obama government, they are starting to believe that we are really changing, but we need to convince the other guys in Congress,” the adviser, Ko Ko Hlaing, said in an interview at a government office in Rangoon.

Although Sunday’s result hardly dents the government-backed party’s huge majority in the Burmese parliament, it means that Suu Kyi will face off against military-backed officials for the first time within the country’s new and evolving political establishment.

U.S. officials said Sunday’s poll, the first involving Suu Kyi in 22 years, represents a significant step, despite reports of some campaign and election irregularities.

“There are tangible moments that demand a tangible response to support ongoing reform,” said a senior U.S. administration official, who was not authorized to speak by name.

But what exactly the United States should offer is still under discussion within the Obama administration, as is a timetable for rolling out such rewards.

The government could offer visa waivers for Burmese officials now banned from traveling to the United States; nominate a U.S. ambassador to Burma, as promised earlier this year; lift minor sanctions by presidential order; or initiate military exchanges.

A more dramatic action would be lifting U.S. sanctions barring foreign investment in Burma and imports from the country — moves that the Obama administration and Congress are unlikely to make until more permanent reforms appear to take hold.

U.S. officials say they are watching to see how the election plays out — first on Sunday, when the results are officially announced, and then later in April, when the new additions to parliament, including Suu Kyi, are seated.

“For now, people on the Hill are open to giving small things that are reversible,” said one congressional aide, who spoke on the condition of anonymity to describe internal discussions in Congress. “I don’t think there’s any appetite yet for lifting the major sanctions.”

The most immediate reward is likely to be visas for Burmese officials. Burma’s health minister, Pe Thet Khin, is scheduled to bring a delegation Sunday to visit Johns Hopkins University to discuss possible public health partnerships, according to those coordinating his visit.

And Burma is making arrangements for a second high-level delegation to Washington to argue its case on sanctions, according to democracy advocates.

Suu Kyi struck a conciliatory tone Monday in Rangoon, telling a small crowd of supporters outside her National League for Democracy headquarters that Sunday’s election had been a triumph, not only for her party but for ordinary voters.

“We hope that this will be the beginning of a new era, when there will be more emphasis on the role of the people in the everyday politics in our country,” she said.

There is no sign that the government plans to annul Suu Kyi’s win, as it did after her emphatic general election victory in 1990. Suu Kyi spent 15 of the next 21 years under house arrest.

Burma, also known as Myanmar, is entering unfamiliar territory, both for Suu Kyi and for a nominally civilian government that remains dominated by the military. The president’s adviser, Ko Ko Hlaing, acknowledged that the government is not used to contesting elections.

“I could guess that the NLD would take the lion’s share in these elections, but I didn’t expect this much of a landslide victory for them,” he said. “The people are quite excited about this electoral process, and they would like to show their mind and hope for change.”

Speaking about the president’s relationship with Suu Kyi, he said that although the two had met in person only once, the leaders representing opposite sides of Burma’s rapidly diminishing political divide had built a strong understanding based on actions rather than words. Representatives of the two sides were in regular contact, he said.

“I think Suu Kyi is using a more conciliatory way to cooperate with the government,” he said. “At the same time, she has the right to move freely in her party political activities, so I think that the government understands her moves and is quite confident they will be within the law.”

The president’s chief adviser said the government remained intolerant of “demanding revolutions to topple the government,” which he likened to the Arab Spring.

Suu Kyi came to prominence in Burma when, as the daughter of the country’s independence hero Aung San, she became the leader of anti-government demonstrations that swept Rangoon in 1988. Since then Burmese activists have intermittently taken to the streets of the country’s largest city, often when Suu Kyi herself has been under house arrest, including in 2007 when demonstrations by monks were brutally suppressed.

Ko Ko Hlaing said that the country will continue to reform as it moves toward general elections at the end of 2015.

Sunday’s election “is the preliminary test for democratic transition, and the general elections in 2015 will be the final exam,” he said.

Wan reported from Washington.