Vientiane - US Secretary of State John Kerry arrived in communist-controlled Laos late on Sunday in a rare high-level visit by an American diplomat to Washington's former wartime foe.
The visit comes ahead of a key summit between President Barack Obama and leaders of the Asean bloc in the US next month - and a landmark trip by the American leader to the tiny, landlocked Southeast Asian nation later this year.
The Communist Party has ruled impoverished Laos since 1975 at the end of the Vietnam War, which split the country and saw it blanketed by bombs in a secret war led by the CIA.
But relations between the two countries have improved with Obama courting the Association of Southeast Nations (Asean) as a diplomatic counterweight to regional power China.
Laos is chair of the 10-member Asean this year and will see a flurry of diplomatic meetings that will open the cloistered, tightly-controlled nation to greater scrutiny.
"After decades of a very difficult relationship between Laos and the US - a period of estrangement, a period of mutual suspicion - there has been increasingly a real transformation in the bilateral relationship," a US State Department official told reporters ahead of the visit.
The US has reached out to its former wartime foe with help clearing unexploded bombs, an issue "that resulted from our actions in the Vietnam War", the official said, as well as through health and education schemes.
In turn, the Lao People's Democratic Republic, has shown "a real interest in diversifying their diplomacy as well as their economy".
US warplanes dropped more than two million tons of ordnance on Laos from 1964 to 1973 in about 580 000 bombing missions aimed at cutting North Vietnam supply lines through the neighbouring country.
An estimated 30% of the ordnance failed to detonate and 50 000 people have been killed by the explosives since the end of the war.
Kerry, a Vietnam War veteran, becomes only the second Secretary of State to visit Laos since the mid-1950s, after his predecessor Hillary Clinton visited in 2012.
Human rights remain a sticking point between the two nations, in particular the disappearance of prominent community activist Sombath Somphone in 2012.
Kerry arrived from Saudi Arabia where he reassured his hosts over the enduring strength of their relationship despite the US warming of ties with Iran.
After spending the day in sleepy Laos capital Vientiane, Kerry will travel to neighbouring Cambodia.
Both Laos and Cambodia are heavily under the influence of China which provides trade and diplomatic ballast to their authoritarian regimes.
In that context, experts say Kerry's trip to two nations with small populations but strong growth rates is laden with symbolism.