US Vice President Kamala Harris arrived in South Korea Thursday to strengthen Washington's alliance with Seoul, a day after nuclear-armed North Korea tested more ballistic missiles.

Harris, who landed at Osan airbase after a trip to Tokyo to attend the state funeral of assassinated former Japanese prime minister Shinzo Abe, is due to meet South Korea's President Yoon Suk-yeol.

She is also set to visit the heavily fortified Demilitarized Zone that separates North and South Korea, a move that would infuriate Pyongyang.

North Korea branded US House Speaker Nancy Pelosi the "worst destroyer of international peace" when she visited the border in August.

North Korea has conducted two banned ballistic missile launches this week ahead of Harris' arrival, one on Sunday and one on Wednesday -- part of a record-breaking streak of weapons tests so far this year.

Speaking aboard a American destroyer at a naval base before she left Japan, Harris accused North Korea of threatening regional stability with fresh missile launches, denouncing their "illicit weapons program".

South Korean and US officials have been warning for months that North Korean leader Kim Jong Un is preparing to conduct another nuclear test, with the South's spy agency saying it could come as early as next month, after China's Communist Party Congress.

The United States and South Korea are conducting a large-scale joint naval exercise this week in a show of force against growing North Korean provocations.

With President Yoon, Harris is set to discuss the countries' long-standing security alliance, their growing economic and technology partnership, and a range of other regional and global issues, her office said.

Seoul's is also likely to raise its concerns over a new law signed by US President Joe Biden which removes subsidies for electric cars built outside of America, hitting Korean automakers like Hyundai and Kia. 

AFP