Money belonging to North Korea that was frozen in a Macau bank - a key issue in nuclear disarmament talks - will reach Pyongyang "very soon", the US has said.
Unblocking the BDA accounts has long been a sticking point
US Assistant Secretary of State Christopher Hill said the $24m (£12.1m) transfer had been delayed by technical problems in the Russian banking system.
And North Korea invited UN monitors to discuss shutting down a key nuclear reactor, state media confirmed.
A row over the funds had stalled the deal agreed in February in Beijing.
The North Korean funds were frozen for nearly two years after the US said they were the result of drug smuggling and counterfeiting, making other banks unwilling to touch them.
On Thursday, Macau government officials said the money had been transferred from Banco Delta Asia (BDA) to the US Federal Reserve.
It was then to be sent on to a North Korean account at a bank in Russia.
Speaking to reporters during a visit to Mongolia, Mr Hill said the funds had been transferred to Russia and that he expected them to be paid into the North Korean account in the next few days.
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"They're having some technical problems in getting it to the bank where the actual North Korean accounts are," he said.
Mr Hill did not provide details of the problems, however, but he said the US had first learned of them from the North Koreans.
The US nuclear envoy said he hoped the transfer would prompt Pyongyang to act on its pledge at the six-party talks to shut down and seal its Yongbyon nuclear reactor.
"We hope they will get on with what they need to do in terms of implementing the February agreement," he said.
North Korea has said in the past that it will begin the process of closing its reactor once it has received its funds.
But after Mr Hill's announcement, a statement on North Korean news agency KCNA said the country's atomic energy chief, Ri Je-son, had written a letter to the director general of the International Atomic Energy Agency, Mohammed ElBaradei inviting UN inspectors.
"He in the letter noted that a working-level delegation of the IAEA has been invited to visit the DPRK [North Korea] as it is confirmed that the process of de-freezing the funds of the DPRK at the Banco Delta Asia in Macau has reached its final phase," the agency said.