South Korean President Yoon Suk-yeol is heading for Washington for a summit with US President Joe Biden, where they are likely to reaffirm strengthening what is known as "extended deterrence" against North Korea.

Yoon began his trip on Monday. The summit is due to take place in the US capital on Wednesday, local time.

This year marks the 70th anniversary of the bilateral alliance. Yoon is the first South Korean president in 12 years to pay a state visit to the United States.

Topics at the summit are expected to include extended deterrence. It means the US commitment to defend its allies with both conventional and nuclear capabilities.

South Korea's Dong-A Ilbo newspaper reported on Monday that the two sides have been working on "a joint document that outlines the conditions for US retaliation with nuclear weapons in the event of a nuclear attack on South Korean territory" by North Korea.

The newspaper also said the document is being coordinated at Seoul's request.

Last week, the South Korean presidential office said the summit will be an opportunity to show the idea of extended deterrence in a more concrete manner.