The United States has clarified the reasons it has imposed sanctions on a Pakistani nuclear facility and a North Korean missile company.
It says North Korea's Changgwang Sinyong Corporation has been involved in a "missile related transfer" to the Pakistanis nuclear facility, Khan Research Laboratories (KRL).
A nuclear missile launch from Pakistan's Khan Research Laboratories
However, the State Department in Washington said the sanctions were not imposed because of any nuclear technology transfers between the two firms.
It was responding to earlier reports that had said the US had imposed sanctions because Pakistan and North Korea had been exchanging nuclear technology.
For the past few days, senior Pakistani officials have been working furiously to counter claims that the penalties imposed by the US on the KRL plant near Islamabad were because of the transfer of nuclear material to North Korea.
Pakistan has long been suspected of trading nuclear technology with the North Koreans in exchange for help in developing its own nuclear-capable missile systems.
Analysts say that in Pakistan's nuclear race with India, developing short, medium and long range missiles is crucial because it is so outclassed in conventional weapons.
Pakistan has consistently denied suggestions that it is involved in the proliferation of nuclear weapons.
The BBC's Paul Anderson in Islamabad says that the US State Department has come to their assistance - to a degree.
A State Department statement says that, regarding the possible transfer of nuclear technology from Pakistan to North Korea, the facts "do not warrant the imposition of sanctions".
However, the State Department says the facts on the transfer of missile technology from North Korea to Pakistan do.
Hence the decision that both KRL and North Korea's Changgwang Sinyong Missile Marketing Corporation be subject to sanctions.
That means the US has banned all contacts with the companies.
Nuclear experts in Pakistan say KRL does not trade with United States companies or institutions, so the sanctions will have little effect.
They say the US move is more a subtle warning from the Americans that nuclear non-proliferation is still a policy priority, whatever else is going on in the world.
Abdul Qadeer Khan - a national hero in Pakistan
KRL's former head is Abdul Qadeer Khan.
Dr Khan became a national hero in Pakistan for his key role in developing the nation's nuclear weapons programme.
He is now an adviser to the government.
Pakistan has, in the past, rejected allegations that it has supported North Korea's nuclear weapons programme.
North Korea is one of the countries branded by the US as part of an "axis of evil".
'Nothing to look at'
Last November, the US said it was satisfied that Pakistan was no longer co-operating with North Korea in supplying nuclear weapons technology.
US Secretary of State Colin Powell said there was nothing at the moment "that has been reported to me that I need to be looking at".
Mr Powell said President Pervez Musharraf had assured him that there were no further contacts of the kind that were referred to in a New York Times report which said Islamabad provided Pyongyang with gas centrifuges and equipment to make highly-enriched uranium.
The report alleged that in return for helping North Korea, Pakistan had received help for its strategic missile programme.