An agreement that would reportedly require North Korea to shut down its nuclear weapons programme within two months appeared closer on Saturday as officials from six nations held a third day of talks.
US chief negotiator Christopher Hill said "basically one or two items" remained to be agreed upon with North Korea.
Hill said he was "cautiously optimistic" after he and his North Korean counterpart Kim Kye Gwan on Friday discussed a draft agreement that reportedly calls for Pyongyang to shut down key weapons-related facilities, including a 5-megawatt nuclear reactor, within two months in return for energy aid.
The draft was circulated late on Thursday after talks resumed between North Korea, the US, China, South Korea, Japan and Russia.
Chinese state media quoted Japan's envoy Kenichiro Sasae as saying as he left his hotel Saturday that the talks had entered "difficult stage."
North Korea remained "highly concerned" with wording in the draft two-page document, the official Xinhua news agency quoted Russia's chief negotiator Alexander Losyukov as saying.
But the New York Times said US State Department and White House officials were "preparing for a major announcement this weekend" in Washington.
South Korean negotiator Chun Yung Woo said Saturday and Sunday would be "decisive" for reaching an agreement.
The draft agreement also proposes setting up five working groups to oversee the process of denuclearisation in North Korea, South Korea's Yonhap news agency quoted sources as saying.
The proposed working groups include one group on the steps to be taken by North Korea to abandon its nuclear programme, another on compensation for Pyongyang, and one to normalise diplomatic relations between North Korea and Japan, Japan's Kyodo news agency said.
Sources told DPA that Hill and Kim had "significantly narrowed" their differences during bilateral talks in Berlin last month.
North Korean officials "showed their readiness" to reciprocate after the US raised the possibility of eliminating trade barriers and removing North Korea from its list of state sponsors of terrorism, a source familiar with the Berlin talks said.
North Korea is reportedly negotiating for some 500,000 tons of fuel oil in exchange for suspending operation of a Yongbyon nuclear reactor and agreeing to IAEA inspections, according to Japanese media.
Host nation China said it was taking an "open attitude" to the duration and content of the talks.
The negotiations were the second since North Korea first detonated an atomic bomb on Oct 9, an event that prompted international sanctions against the Stalinist state.
North Korea in September 2005 agreed to give up its nuclear weapons programme in return for security guarantees from the US and economic aid.