America and South Korea agreed to increase military exercises in response to the North’s threat, while offering Pyongyang assistance to combat its COVID-19 epidemic.
Biden visited the country to meet his South Korean counterpart Yoon Suk Yeol. He was inaugurated 11 days earlier.
The discussions were dominated by tensions with North Korea, and fears that it might launch new missile tests.
In a joint statement Mr Biden reiterated the US commitment to defend South Korea with nuclear weapons if necessary.
Both sides agreed to expand their joint military drills. These had been reduced in recent years to try to improve relations with the North.
North Korea could react angrily to the idea of larger exercises among allies.
Pyongyang defends its nuclear weapons and missile production on US threats. It has long called the drills invasion rehearsals. However, the US and South Korea insist that they are defensive.
The US also pledged to deploy “strategic assets”, which include long-range bomber planes, submarines and aircraft carriers, if necessary.
Both leaders insist they are open to diplomatic talks with Pyongyang
Mr Biden stated that deciding whether or not to meet with North Korean leader Kim Jong Un would depend on his sincerity and his seriousness.
He also disclosed that Washington had provided COVID-19 vaccinations to China, North Korea and North Korea in an effort to combat its first recognized outbreak.
“We have no response,” said Mr Biden.
Seoul offered its assistance to the North, which has been ignored.
North Korea has reported that more than 200,000 people have “fever” in the fifth consecutive Saturday. However, there are no vaccines or modern treatments for the pandemic.
The refusal to offer assistance has lowered hopes that such cooperation would help to ease nuclear tensions, or even lead to negotiations.
North Korea’s missiles have been tested 16 times this year, including March when it launched its first intercontinental ballistic missile since 2017, demonstrating a range that could reach the entire US mainland.
The Biden administration has asked China to refrain from further testing.