North Korea said nothing about opening its nuclear facilities at Yongbyon until the American delegation had already left the country.
Opening the door to Yongbyon's facilities is seen as a big step
It then released a brief statement saying it had shown what it called a "nuclear deterrent force" to its guests.
The Foreign Ministry said it had been compelled to build a deterrent because of United States policy.
The Americans, including an academic, a nuclear scientist and congressional aides were given all requested access.
But the US inspectors said they would not give details of their findings until they had briefed the administration.
North Korea began referring to its "deterrent" last year after it expelled UN monitors from Yongbyon.
Until then it had always insisted that its nuclear programme was for peaceful purposes.
There has been massive media interest in the US visit to facilities
The Foreign Ministry statement said the aim of the visit was "to give Americans an opportunity to confirm the reality by themselves".
It said if it helps the US drop its ambiguous view on the North's nuclear activities it could help bring a peaceful solution.
North Korea claims in recent months to have reprocessed 8,000 spent fuel rods that were extracted from the reactor a decade ago, and which would produce enough plutonium for about six atomic bombs.
The North seems intent on proving to the United States that it is not bluffing about its nuclear capabilities.
It has been frustrated by Washington's apparent lack of urgency and its refusal to negotiate directly.
Last week North Korea repeated an offer to freeze its nuclear programme in return for economic aid and an end to sanctions from Washington.
US intelligence has been watching from the air for years
That was seen as a sign that the North was serious about dialogue.
But the United States continues to insist that the regime give up its nuclear ambitions for good and scrap all its nuclear facilities.
The United States has estimated for a decade that North Korea already has two nuclear weapons.
But convincing evidence that the regime is building a more substantial arsenal would be seen as a serious escalation.
North Korea has threatened in recent months to test or even sell a nuclear device.
The United States has been trying to work with regional powers to convince North Korea to abandon its weapons programme.
It is hoping for a new round of negotiations in Beijing in February, despite the failure to make progress at a first session last August.
North Korea is trying to inject more urgency into the process to force concessions from the United States.
South Koreans continue to vent their anger at the regime in the North
But it is taking a substantial risk.
The Bush administration remains deeply divided over how to deal with North Korea.
Influential figures in the administration have never been convinced of the value of dialogue.
Some see regime change as the only long-term solution and have argued for sanctions and a naval blockade to force it into submission.
Much will depend on how convincing the North Koreans were during last week's presentation at the Yongbyon facility.