A senior Pakistani nuclear scientist has gone home after being questioned about his work at the country's main nuclear laboratory, officials say.
Pakistan launched a nuclear missile from Khan Research Laboratories
He was one of two scientists understood to have been brought in for questioning between one and two weeks ago.
A Foreign Ministry spokesman denied they been arrested saying they were being "debriefed".
He also dismissed speculation that the issue was linked to alleged transfers of nuclear know-how to Iran.
"The debriefing session of one of the scientists has concluded and he has resumed his normal duties," the spokesman, Masood Khan, told the AFP news agency.
News that two of Pakistan's leading nuclear scientists had been called in for questioning surfaced on Wednesday, when senators in Pakistan's upper house of parliament walked out in protest at what they called the men's arrest.
The senators described the affair as a national insult.
Mr Khan said Pakistan had a policy of not exporting nuclear expertise to any country, but intelligence officials' allegations that skills have been transferred to Iran - raised in the Western media - refuse to go away.
They have also alleged Pakistan shared nuclear know-how with North Korea.
The men are senior staff at Pakistan's uranium-enrichment facility, the Khan Research Laboratories.
Opposition leaders said the two played a key role in Pakistan's successful nuclear bomb tests in 1998.
Earlier this year, the Americans imposed sanctions on the Khan Research Laboratories, saying the establishment was providing material support to a country or people trying to develop weapons of mass destruction.
The allegation was denied in Pakistan.