Biden made the comments are a press conference after receiving his South Korean counterpart Moon Jae In at the White House, dpa reported.
Talks with Pyongyang must focus on "pragmatic steps that will reduce tensions as we move toward our ultimate goal of denuclearization of the Korean Peninsula," Biden said.
"We are under no illusions how difficult this is," Biden said.
Biden also announced the appointment US diplomat Sung Kim as a North Korea envoy.
Moon welcomed the appointment and the US government's willingness to work diplomatically to denuclearize the Korean Peninsula.
"I have high expectations," he said in translated remarks.
"The most urgent common task that our two countries must undertake is achieving complete denuclearisation and permanent peace on the Korean Peninsula," he added.
Biden promised the US would work closely with South Korea on the approach towards Pyongyang.
He called the "ironclad" alliance with Seoul the "linchpin" of peace, security and prosperity in the region.
Moon is in his final year in office, and his opportunity to advance peace with the North running short. Meanwhile Biden is confronting a goal that has eluded predecessors stretching back to Bill Clinton: stamping out Pyongyang's nuclear programme.
North Korea's rogue regime test-fired short-range missiles in March. It was seen as a challenge to the new Biden administration and propelled Pyongyang to one of the president's most pressing foreign policy issues.
US Secretary of State Antony Blinken and Pentagon boss Lloyd Austin travelled to Seoul in recent months as part of Washington's efforts to coordinate strategy with the South.
Moon's trip to the White House marked only the second visit by a foreign leader since Biden took office in January.
In April, Biden hosted Japanese Prime Minister Yoshihide Suga, another key ally for Washington in East Asia.
Biden has promised "responses" if North Korea escalates, but has not offered a detailed outline of his approach beyond efforts to pursue talks with North Korea.
Former US president Donald Trump engaged in face-to-face diplomacy with North Korean ruler Kim Jong Un, with whom he had a famously hot and cold relationship.
White House Press Secretary Jen Psaki was asked by a reporter on Thursday if a Biden-Kim encounter was possible.
"I don't expect that to be top on his agenda," she said.
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