In a practical sign of improving ties, the two signed an "open-skies" agreement allowing access to each other's airlines, which officials said may give a small boost to tourism in isolated and landlocked Laos.
Ties between the US and Laos have long been tense over concerns of human rights abuses of the ethnic Hmong minority along with uncertainties over US troops missing in action.
"The United States is committed to building our relationship with Laos as part of our broader efforts to expand engagement with Southeast Asia"
Philip Crowley, US State Department spokesman
Many Hmong fighters assisted US forces during the Vietnam War, and rights groups say the community has faced persecution from the country's communist government.
The US established normal trade ties with Laos in 2004 and has recently looked at ways to help clear unexploded landmines that continue to take a heavy toll on the country.
During the war US forces dropped millions of bombs on the country to cut off North Vietnamese supply lines, but many failed to immediately explode and a recent survey estimated that some 50,000 Lao civilians have died in the years since.
Philip Crowley, spokesman for the US state department, said that Clinton and Thongloun discussed "a wide range of old and new areas for bilateral co-operation".
"The United States is committed to building our relationship with Laos as part of our broader efforts to expand engagement with Southeast Asia," he told reporters.
Some 250,000 Hmong have resettled in the US since the war and often speak of persecution in Laos, enlisting support of US legislators to pressure the Vientiane government.
The revived US interest in Laos comes as China expands its influence in the country, as well as across Southeast Asia.
China has been seeking to improve relations with Laos, with Chinese vice-president Xi Jinping visiting the country last month and pledging millions of dollars of investment in infrastructure.
|US forces dropped millions of bombs on Laos during the Vietnam War
Last year the US initiated a dialogue with another isolated Southeast Asian country, Myanmar – formerly known as Burma - whose military government has curtailed the rights of the democratic opposition.
Ernie Bower, the head of the Southeast Asia programme at the Centre for Strategic and International Studies, said Tuesday's talks in Washington marked a US effort to "broaden and deepen engagement" with countries in the region.
He said the Laotian government knows of the interest groups in the US, like the Hmong, who are out "to pressure them on issues they just don't want to talk about".
"The Lao were a little nervous about taking the diplomatic risks of reaching out their hand, but now they are starting to see a little return," said Bower, pointing to growing US business in Laos since restrictions were lifted.