A key US senator on Tuesday backed an end to US sanctions on Myanmar after a landmark visit by the country's reformist leader, signaling a new normalization in relations despite rights concerns.

President Thein Sein, a general-turned-civilian who ended Myanmar's long isolation from the West, met lawmakers at the US Capitol one day after the first White House summit by a leader of his country in nearly 50 years.

Senator Mitch McConnell, who has spearheaded sanctions for the past decade over human rights concerns, said he would not support a renewal of the measures that banned a range of imports from the country formerly known as Burma.

"I believe renewing sanctions would be a slap in the face to Burmese reformers and embolden those within Burma who want to slow or reverse reform," McConnell, the Senate Republican leader, said after meeting Thein Sein.
President Barack Obama has already waived most sanctions on Myanmar but Congress has kept the laws on the books, hoping that the threat of reimposing the restrictions would motivate the government to address concerns.

McConnell, who said he gave the issue "a great deal of thought," said that a ban on gems -- a key revenue source for the junta -- would remain and that the end of sanctions would put US firms on the same level as Europe and Australia.

But Thein Sein also met separately with four House members from President Barack Obama's Democratic Party, who handed him a list of nearly 250 inmates allegedly jailed for political reasons and urged an end to ethnic violence.

The prisoners "deserve the opportunity to participate in the future of the country, and we believe they should be released immediately and unconditionally," the lawmakers said in a letter handed to Thein Sein.

The lawmakers included former speaker Nancy Pelosi and Joe Crowley, who has reintroduced a sanctions bill in the House.

Thein Sein has released hundreds of political prisoners since taking office in 2011. He has also eased censorship, opened talks with rebels and allowed long-detained opposition icon Aung San Suu Kyi to serve in parliament.

Adding to the historic symbolism of the visit, the leader of the nation formerly known as Burma took a short side trip to tour the Mount Vernon estate of US general-turned-first-president George Washington.

The United States and Myanmar on Tuesday also signed an accord to formalize dialogue on trade, a day after Thein Sein surprised US business leaders by making a pitch in good English for investment in poor but growing Myanmar.

Derek Mitchell, the US ambassador to Myanmar, hailed Thein Sein's reforms as having "captured the imagination of Americans" but said that his visit was not the end.

"Beyond the euphoria of new hope and rising expectations is the reality of the hard work to come," Mitchell told a dinner in Thein Sein's honor at the US Chamber of Commerce.

"I know of no one in your government -- or mine -- who is declaring victory as if the future course of your country is clear and inevitable," Mitchell said.

Critics say Obama's invitation to Thein Sein left few US incentives to offer in return for action on other concerns, including addressing anti-Muslim violence to which security forces were accused of turning a blind eye or worse.

The most important test will come in 2015 when Myanmar is scheduled to hold elections, meaning that the military may have to decide whether it will truly cede power for the first time since seizing control in 1962.

Thein Sein, who had served as premier under the former junta, was asked repeatedly in Washington about the military and defended the armed forces as playing a critical role.

Walter Lohman, director of the Asian Studies Center at the conservative Heritage Foundation, said the Obama administration appeared to be moving from a policy of maintaining leverage on Myanmar to one of supporting Thein Sein.

"I don't know that our assistance or support for him is really going to help him, but I think it does potentially send the wrong signal back to people in Burma who are still struggling," Lohman said.

"If we get to 2015 and (a free election) doesn't happen, we will have been wrong about all this," he said.