A US Treasury delegation is in Macau to discuss lifting sanctions imposed on a bank in the Chinese territory accused of helping North Korea launder money.
An official said the treasury was ready to "begin taking steps" to settle the dispute over Banco Delta Asia.
The sanctions, imposed last year, led to the freezing of some $24m of North Korean funds.
The North insisted the issue be dealt with as part of nuclear talks which saw a breakthrough on 13 February.
Under the agreement, North Korea agreed to "shut down and seal" parts of its nuclear programme in exchange for aid, ahead of the programme's eventual abandonment.
South Korea said on Monday that preparations were under way to send $20m worth of fuel oil shipments to the North, as one of the first steps under the agreement.
The announcement came a day before the two Koreas resumed ministerial talks in Pyongyang.
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