Hillary Clinton on Wednesday became the first US secretary of state to visit Laos for 57 years, on a trip focused on the damaging legacy of the Vietnam War. 

The US "desire was to deepen and broaden" the relationship, Clinton said after a visit to a US-funded orthotic and prosthetic center, which she described as a "painful reminder of the legacy of the Vietnam War era". 

"Here in Laos the past is always with you," she said, addressing US embassy employees. 

US forces dropped more than 2 million tons of ordnance on Laos between 1964 and 1973 in some 580,000 bombing missions to cut off North Vietnam supply lines. 

Some 30 percent of the ordnance failed to detonate. All 17 of the country's provinces are still contaminated by unexploded ordnance and Laos remains the most heavily bombed country, per capita, in history. 

Clinton, making a four-hour whirlwind trip, met Prime Minister Thongsing Thammavong at his office in an elegant white-columned building with two large elephant statues outside. 

The pair had "substantive discussions on the broadening bilateral cooperation", according to a joint statement released after the meeting. 

The countries "agreed to improve and further facilitate the accounting operations for US personnel still missing from the Indochina War era" and address the "remaining challenges" of unexploded ordnance, the statement said. 

They also discussed the forthcoming entry of landlocked Laos, one of the poorest nations in the world with just 6.5 million people and annual GDP growth of 7 percent, into the World Trade Organization. 

Clinton is only the second secretary of state to visit Laos after John Foster Dulles, who spent a day in the then-monarchy in 1955. 

US relations with Laos, while never severed, were long tense, in part over its campaign against the Hmong hill people who assisted US forces during the Vietnam War. 

But the United States established normal trade ties with Laos in 2004 and annual US aid to Laos will be around $30 million in total for 2012, a US embassy official said. 

Of that, $9.2 million will be set aside this year for cleaning up unexploded ordnance. According to official figures, there has been a fall in accidents involving such munitions from 300 a year to roughly 92 in 2011. 

Clinton said she hoped in the future there would by ways "to give people and particularly children of this nation the opportunity to live their lives free of these unexploded bombs". 

Agence France-Presse