Khai's visit prompted protests by Vietnamese living in the United States, including heckling on Sunday from a group of about 300 in Seattle who called for Khai to leave the country and carried signs likening him to ousted Iraqi president Saddam Hussein.
The visit comes 30 years after US forces pulled out of Vietnam and 10 years after the two countries normalised relations during president Bill Clinton's administration.
Khai, 71, was scheduled to meet President George Bush on Tuesday at the White House. He also planned a Monday meeting at Microsoft headquarters in Redmond, Washington.
At a news conference in a hotel in downtown Seattle, Khai said Vietnam will continue working with the US to strengthen its economy.
"Despite differences on sensitive issues, it should be noted that there are not major differences between the two countries," he said through an interpreter.
World trade group
Khai is seeking Bush's help in gaining Vietnam's admittance to the World Trade Organisation.
In the 10 years since diplomatic ties were restored, the US has become Vietnam's top trading partner, with American investment in the Southeast Asian nation rising 27% each year since a bilateral trade agreement took effect in 2001. The two-way trade was worth $6.4 billion last year.
Khai said increased economic development in Vietnam will improve people's lives and bring stability to Southeast Asia, and asked Vietnamese living in the US to help strengthen the connection between the two countries.
Vietnam Airlines will buy four
Boeing 787 jetliners
"It is our government's consistent policy to consider the Vietnamese community living abroad as an important and integral part of our nation and our resources," he said.
Demonstrators gathered across the street from the hotel and later blocked the road outside, waving banners and the old gold-and-crimson flag of South Vietnam. They shouted "Down with communists" and held signs that read "Khai is another Saddam Hussein".
Nhein Le of Kent, Washington, a former officer in the South Vietnamese air force, said the demonstrations were intended to let Khai know that Vietnamese-Americans wanted him to address the human rights abuses that they charge continue in Vietnam 30 years after the war.
"Compared with all the countries in Southeast Asia, we are at the bottom. That's why we fight for the freedom," Le said.
"We have put the past behind us"
Phan Van Khai,
Vietnamese prime minister
Khai said Vietnamese people should heal the wounds left from war with the US and said Hanoi had worked to address concerns about human rights abuses.
"If they come back to the homeland and have returned, in reality, they will have different views," Khai said.
That answer prompted an outcry from Binh Quoc Huynh, a Nazarene minister from Portland, Oregon, who said he wrote for the Vietnam News Network. Huynh was escorted from the news conference after calling Khai a liar and a murderer.
Khai's first stop on Sunday was Boeing's plant in Renton, south of Seattle, where he was to oversee the purchase of four Boeing 787 jetliners by Vietnam Airlines. He visited a local Vietnamese family before heading to Seattle.
Chris Flint, a Boeing sales director for Asia, said Vietnam's airline has shown annual growth of more than 20% in the past seven years. Such success has helped the country improve life for its citizens, he added.
"You see a lot of improvements from where they were," Flint said.
In an earlier interview in Hanoi, Khai said his visit showed "that we have put the past behind us".
"We're hoping to further tap the potential for even better relations between the two countries based on respect and mutual interest," he said.
"We're hoping to further tap the potential for even better relations between the two countries based on respect and mutual interest"
Phan Van Khai,
Vietnamese prime minister
But the US-based Human Rights Watch urged the US to raise questions about Vietnam's civil rights record. The group said it had documented cases of abuses by the communist government, including the arrests of dissidents for promoting democracy or human rights.
Hundreds of thousands of Vietnamese have settled in the US since communists gained full control of Vietnam. More than 1 million now live in the US.