"The shutdown is something that can be done immediately and it won't take long," Ri Kyong Son, vice spokesman at the ministry, told APTN in an interview in Pyongyang.
North Korea missed an April deadline to close the Yongbyon nuclear reactor under a February agreement with the United States and four other countries, but has said its commitment to the deal remains unchanged.
The North's key precondition to move on disarmament is the release of about $25 million, frozen after Washington blacklisted a Macau bank where the North Korean regime held accounts.
Washington helped unfreeze the funds to win the North's promise to start dismantling its nuclear weapons programs, but technical issues have stalled the transfer.
Ri said he could not predict when North Korea would access the money.
"The U.S. has made the announcement, but only when we receive the funds can the sanctions be said to have been lifted," Ri told APTN. "Making the announcement itself does not settle the unfreezing of the funds."
The North's funds were frozen at the Macau bank — Banco Delta Asia — after Washington blacklisted the institution in 2005 for allegedly aiding the communist regime in money laundering and counterfeiting.
Because of the funds issue Pyongyang boycotted talks on its nuclear program for more than a year, during which it conducted its first-ever test of a nuclear bomb last October.
Despite the money now being freed for withdrawal, the North has had trouble finding a bank to accept it, due to worries that handling the tainted funds could affect business.
A South Korean newspaper reported Monday that Seoul is considering letting the North use a state-run South Korean bank to transfer the funds.
A security ministers' meeting at the presidential office last week discussed giving North Korea an account with the South's Export-Import Bank of Korea so that the communist nation can transfer the funds there, the Chosun Ilbo newspaper reported.
The presidential Blue House, asked about the report, said Monday that South Korea "studied what it can do to help resolve" the financial dispute. "However, consultations are now progressing between the directly related parties and we expect the issue will be resolved through them," it said. It did not elaborate.
Meanwhile, the North's Foreign Ministry also expressed optimism that a scheduled test run of trains across the border separating North and South Korea would go forward later this month. "Testing the running of the train between North and South is expected to be held soon," Ri told APTN.
However, it was unclear if the North's military has agreed to the plan. Such tests have been scheduled before only to be called off at the last minute due to the objections of the North Korean military, citing security concerns.
The two Koreas are scheduled to open military talks Tuesday to discuss the issue.