The two countries want to put the past behind them
South Korea and its former Cold War foe, Vietnam, have pledged to strengthen ties during the start of a landmark visit to South Korea by Vietnamese President, Tran Duc Luong.
It is the first such visit by a Vietnamese leader since the end of the Vietnam War.
During talks with South Korean president, Kim Dae-jung, the two leaders signed a joint declaration in which they agreed to expand bilateral ties.
When the two countries formed diplomatic ties nearly 10 years ago they pledged to work for a future oriented relationship.
And at the start of his visit, President Luong emphasised that the painful past would be set aside. Around 300,000 South Korean troops fought alongside US forces during the Vietnam War.
For his part, President Kim expressed regret that his country's involvement in the war had caused pain and said South Korea was determined to overcome their unhappy past.
Oil find
In their joint declaration, called a comprehensive partnership for the 21st century, they agreed to boost exchanges, including the economy, tourism, the arts and sport. They also agreed to annual meetings between their foreign ministers.
Until now, the bilateral relationship has been largely economic. South Korea is one of Vietnam's biggest foreign investors and trading partners. Two-way trade amounted to $2bn last year.
That could be boosted by the announcement made during the state visit that a South Korean-led consortium, which has been exploring for oil in Vietnam, has made a significant discovery of commercially viable oil deposits off the country's south-eastern coast.
The two leaders attended a ceremony celebrating the oil discovery. South Korea says it is willing to assist with future projects.
President Luong is due to meet business leaders and tour industrial facilities before leaving South Korea on Saturday.