The high-level meetings at the U.S. Mission to the United Nations, in the shadow of the U.N. headquarters complex, have raised hopes of a possible breakthrough in resuming disarmament negotiations after more than a year of high tensions between the rival North and South.
The discussions aim to build on last week's surprise talks between nuclear negotiators from North and South Korea in Indonesia, the first such meeting since disarmament talks were last held in December 2008. The arms talks collapsed shortly afterward.
Seoul blames Pyongyang for two attacks last year that killed 50 South Koreans and led to threats of war.
Ambassador Stephen Bosworth, the Obama administration's top envoy on North Korean affairs, will head the U.S. delegation in talks Thursday and Friday with North Korean Vice Foreign Minister Kim Kye Gwan, the State Department said.
Gwan arrived at the U.S. mission Thursday morning and shook hands with Bosworth in the doorway. He did not speak to reporters waiting outside.
"We're not prepared to have talks for talks' sake," State Department spokesman Mark Toner told reporters in Washington on Wednesday. "What we're looking for in this meeting is to determine if North Korea is, in fact, ready to fulfill its commitments."
That was a reference to a 2005 joint declaration requiring North Korea to abandon all nuclear weapons programs and allow the return of international weapons inspectors in exchange for better relations with its Asian neighbors, energy assistance and a pledge from Washington that it wouldn't attack the North.
Toner said the United States was only engaging in "exploratory" talks.
Five nations - the United States, China, Japan, South Korea and Russia - have been negotiating since 2003 to persuade North Korea to dismantle its nuclear programs. Pyongyang pulled out of the six-party talks in April 2009 after being censured for launching a long-range rocket.
However, North Korea and China have made recent calls to resurrect the negotiations.
Kim told reporters after landing in New York Tuesday that he was "optimistic" the six-party talks could resume and that relations with the U.S. might improve.
"Now is the time for countries to reconcile," he said, according to South Korea's Yonhap News Agency.
On Wednesday, Pyongyang pressed for the U.S. to sign a peace treaty formally ending the Korean War. In an editorial marking the 58th anniversary of an armistice ending the 1950-53 conflict, the official Korean Central News Agency repeated a long-held demand of the North Korean government, saying a peace treaty could help resolve the nuclear deadlock.
At U.N. headquarters, North Korea's Ambassador Sin Son Ho said Wednesday that U.S. modernization of its nuclear weapons and expansion of its missile defense systems will eventually spark a new nuclear arms race.
He told a General Assembly meeting on revitalizing the Conference on Disarmament, which North Korea chairs this month, that if "the largest nuclear weapon state" - a reference to the United States - wants to stop the spread of nuclear weapons "it should show its good example by negotiating the Treaty of Abolishing Nuclear Weapons."
Sin said North Korea's "consistent policy" is "the total and complete elimination of nuclear weapons."
But he said modernization programs, including making small nuclear weapons that can be used like conventional weapons and expanding missile defense systems to blanket the globe, show that the U.S. "has lost its legal or moral justifications to talk of proliferation issues."
The U.S. Mission to the United Nations did not immediately respond to a request for comment on Sin's statement.
The cautious diplomatic jostling ahead of the talks came after more than a year of hardline unity by Washington and Seoul, backed by international investigators who concluded that a North Korean torpedo sank a South Korean warship in March 2010, killing 46 sailors.
The South demanded an apology from the North for that incident, and an artillery attack on a front-line South Korean island that killed four in November.
North Korea denies a role in the sinking and says South Korea provoked the island shelling with a firing drill. At the same time, Pyongyang repeatedly has shown a willingness to return to the disarmament table. The North is seen as needing a diplomatic breakthrough and outside food aid ahead of the 2012 centennial of the birth of the country's founder, Kim Il Sung.
Secretary of State Hillary Rodham Clinton invited the North Korean vice foreign minister to New York after what U.S. officials described as a constructive meeting between North and South Korean negotiators at an Asian security forum last week. But Clinton said the U.S. wouldn't reward the North for just returning to the table or promising to uphold old agreements.
The wariness reflects years of U.S. frustrations with North Korea, which has used its nuclear program to wring concessions from Western nations. The U.S. also said ally South Korea needed to be satisfied with the North's sincerity before Washington would act.
Associated Press Writer Anita Snow contributed to this report from the United Nations