Leader Kim Jong-Il gave the commitment at a meeting late Monday with visiting Chinese Premier Wen Jiabao, the North's official news agency reported.
Highlighting the issue, a South Korean source said the North appeared to be in the final stages of restoring plutonium-producing plants that it had shut down before abandoning the six-party process.
"The hostile relations between the DPRK (North Korea) and the United States should be converted into peaceful ties through the bilateral talks without fail," the agency paraphrased Kim as saying.
"We expressed our readiness to hold multilateral talks, depending on the outcome of the DPRK-US talks. The six-party talks are also included in the multilateral talks."
Kim said the North's efforts to denuclearise the Korean peninsula remain unchanged. The official Xinhua news agency in China, which hosts the six-party forum, said the two leaders reached "vital consensus" on the issue.
Some analysts said the North did not want to snub China, its biggest trade partner and chief energy supplier, and Pyongyang's willingness to scrap its cherished nuclear programme remains questionable.
The North Koreans "are clearly trying to mend relations with China and show appreciation for its economic assistance," said Peter Beck, senior researcher at Stanford University in the United States.
"But the North has left itself a lot of wiggle room to back out of the talks if it feels it's not getting what it wants," he told AFP.
"Given the North's recent strong statements about the need for its nuclear programmes, I find it hard to believe it's ready to give them up any time soon."
The North has lately linked denuclearisation of the Korean peninsula to the pace of global atomic disarmament efforts, and says it needs atomic weapons as a shield against US hostility.
It quit the six-nation forum in April after the United Nations condemned its long-range rocket launch.
In May the North staged its second nuclear test, incurring tougher UN sanctions supported even by close ally China.
The North has long been pressing for bilateral talks with the United States to end the nuclear standoff.
The US State Department reiterated it is ready for discussions aimed at bringing the North back to the six-nation talks, but the goal must be a complete end to Pyongyang's nuclear programmes.
"We and our six-party partners want North Korea to engage in a dialogue that leads to complete and verifiable denuclearisation of the Korean peninsula through irreversible steps," said spokesman Ian Kelly.
The talks, which began in 2003, group the two Koreas, China, the United States, Russia and Japan. The forum reached deals in 2005 and 2007 under which the North shut down its plants at Yongbyon and began disabling them.
After quitting the talks the North vowed to reverse the process.
"There are signs that the restoration of the Yongbyon facility is in its final stage," the South Korean defence source told Yonhap news agency, citing intelligence reports presented at a parliamentary hearing this week.
Wen's three-day visit, which ended Tuesday, was officially described as a goodwill trip to celebrate the 60th anniversary of diplomatic relations. But Beijing is eager to bring Pyongyang back to nuclear negotiations.
Kim took pains to welcome his guests, greeting Wen with a hug at an elaborate red-carpet airport welcome on Sunday.
On Monday he escorted them to a special performance of the Arirang mass gymnastics display marking the anniversary.
Performers and audience "broke into cheers of 'Hurrah!' shaking the stadium and fireworks were displayed to beautifully decorate the nocturnal sky of the capital city," the North's news agency reported.