Nuclear envoys of the rival Koreas both addressed a closed-door conference on security in Northeast Asia on Thursday but there was no word on whether they spoke to each other.

The two-day, academic forum in New York is an opportunity to break the ice between communist North Korea and U.S.-allied South Korea, which in turn could nudge forward efforts to restart long-stalled, six-nation talks on the North's nuclear program.

But while Pyongyang is striving to improve ties with the U.S., which it sees as important for securing aid and moving toward its ultimate goal of normalized relations, there's no sign it wants to do the same with Seoul. Tensions remain high on the divided Korean Peninsula.

The U.S. and South Korea staged military exercises in recent days, and in apparent response, North Korea held its own drills and called for a ``sacred war'' against the South. Two military attacks on South Korea in 2010 that killed 50 people nearly triggered a war.

North Korea's representative to the six-nation disarmament talks, Ri Yong Ho, and his South Korean counterpart, Lim Sung-nam, are among several dozen participants of the conference at a hotel near the United Nations headquarters. Former U.S. Secretary of State Henry Kissinger and former Deputy Secretary of State Jim Steinberg have also taken part, but no currently serving U.S. government officials.

Organizers barred media from the discussions.

Such informal ``track 2'' talks offer a chance for policymakers and experts to exchange views outside the more constrained atmosphere of formal negotiations. This gathering has attracted extra scrutiny, coming a week after North Korea agreed to a freeze in nuclear activities and to allow in U.N. inspectors in return for U.S. food aid.

John Kerry, the Democrat chairman of the U.S. Senate Committee on Foreign Relations, is expected to speak at the conference before it ends Friday. Another ``track 2'' meeting organized by a different group is scheduled for Saturday.

In Beijing on Thursday, the U.S. and North Korea held more talks to finalize the 240,000 tons of aid, the first such assistance Washington has offered Pyongyang in three years. U.S. envoy on North Korean human rights issues, Robert King, said administrative issues on deliveries of the aid have been resolved, though details still remain to be settled.

The U.S.-North Korean accord is the most substantive sign of warming ties since the North pulled out of the six-party talks in 2009 and ramped up its nuclear and missile programs. The accord was announced little more than two months after the Dec. 17 death of longtime leader Kim Jong Il, succeeded by his untested youngest son, Kim Jong Un.

The U.S. is now watching to see Pyongyang makes good on its commitments to freeze uranium enrichment and allow in U.N. nuclear inspectors. Washington also says that there won't be a fundamental change in U.S.-North Korean relations unless inter-Korean ties improve.

The U.S. retains nearly 30,000 troops in South Korea, as a deterrent against aggression by North Korea, a legacy of the 1950-53 Korean War that ended without a formal peace treaty.

South Korean Foreign Minister Kim Sung-hwan was also in New York Thursday, and met with U.N. Secretary-General Ban Ki-moon but did not attend the security conference.

Kim is due to meet with U.S. Secretary of State Hillary Rodham Clinton in Washington on Friday.(AP)