International nuclear talks are still on track despite a boycott by North Korea on Tuesday over $25 million of its funds frozen in a Macau bank, the chief U.S. delegate said.

The North's main negotiator refused to participate in a meeting of top envoys earlier in the day until all the money was released, Japan's representative said.

But Assistant Secretary of State Christopher Hill characterized the day's progress as "kind of slow" but expressed optimism that the issues would be resolved.

"I think we're still on track," Hill told reporters late Tuesday.

Japan's main envoy, Kenichiro Sasae, said a meeting of the chief delegates of the six nations involved in the disarmament talks was canceled because Pyongyang refused to attend.

"There was no progress at all today," Sasae said. "China as chairman (of the talks) urged North Korea to come to the table but they would not come."

The talks by envoys from the two Koreas, the United States, Japan, Russia and host China resumed Monday shortly after the United States announced that a key sticking point — North Korean funds frozen in the Macau lender Banco Delta Asia — had been resolved.

U.S. Deputy Assistant Treasury Secretary Daniel Glaser said Monday that the money would be transferred into a North Korean account at the Bank of China in Beijing to be "used solely for the betterment of the North Korean people."

The Monetary Authority of Macau, a Chinese territory, said in a statement that it will release the funds "in accordance with the instructions of the account holders" but did not elaborate.

It is not known if there has been a delay in the transfer or when it could take place.

"According to China, North Korea said they will not come to join further discussions until they confirm that their money got into their bank account in China," Sasae said.

But a South Korean official, speaking on condition of anonymity because of the sensitivity of the talks, said he did not expect the problem to linger.

"These issues are expected to be resolved as early as tonight or tomorrow morning," he said. "We expect to begin substantial negotiations tomorrow."

North Korea boycotted the nuclear talks for more than a year after the U.S. alleged it was using Banco Delta Asia to launder money and process counterfeit currency.

The talks are aimed at dismantling North Korea's nuclear program.

Under a hard-won Feb. 13 agreement, Pyongyang has until April 14 to shut down its main reactor and a plutonium processing plant, and to allow U.N. monitors to verify the closures. In return, the regime is to receive energy and economic assistance, and a start toward normalizing relations with the U.S. and Japan.

Hill has said one of the priorities for the U.S. will be to achieve greater clarity on Pyongyang's alleged uranium enrichment program, which the North has never publicly acknowledged having.

Monitor the nuclear showdown on the Korean Peninsula in FOXNews.com's North Korea Center.

Hill also said he and his North Korean counterpart, Kim Kye Gwan, would discuss Pyongyang's strained ties with Tokyo, which have complicated the negotiations.

All parties agree the North's disarmament must be irreversible and the inspections to verify the shutdown will be vital, South Korean envoy Chun Yung-woo said.

"If there is a single nuclear weapon left in North Korea, it is not denuclearization," Chun said. "What we are pursuing is a complete denuclearization."

Under the agreement, North Korea is to receive assistance equivalent to 1 million tons of heavy fuel oil if it fully discloses and dismantles all its nuclear programs.

South Korea has promised to deliver an initial disbursement of energy aid to the North — 50,000 tons of heavy fuel oil — to coincide with the arrival of U.N. inspectors to verify the Yongbyon reactor has been shut down.

Hill said further deliveries would be contingent on what the inspectors find in North Korea.

The South Korean official said Hill and South Korean nuclear envoy Chun Yung-woo met separately with Kim on Tuesday.

"North Korea reaffirmed its commitment to fully implementing the Feb. 13 agreement," the official said of the Hill meeting, adding Kim told Chun he "expected things to go well" regarding the frozen funds.

There was no other immediate confirmation of the meetings.

On Tuesday, North Korean state media accused Japan of trying to scuttle the nuclear talks by raising the issue of the abduction of Japanese citizens by Pyongyang in the 1970s and '80s.

In Vietnam earlier this month, talks between the two sides on normalizing ties ended without progress. North Korean negotiators reacted angrily to Japan's insistence that they must resolve the issue before taking steps to improve relations.

The North's official Korean Central News Agency said Japan should drop the abduction issue and instead apologize to and compensate Pyongyang for its wartime aggression.

Japan has said it will not contribute energy assistance to the North until there is progress on the abduction issue, but KCNA insisted Pyongyang doesn't want aid from Japan.

The North "has never asked Japan for any assistance and it has no idea of getting any help from it, either," KCNA said.

Complete coverage is available in FOXNews.com's North Korea Center.