The Swiss authorities say an investigation into a global nuclear smuggling ring is back on track after the United States handed over legal documents.
Swiss prosecutors waited for over a year for the US to comply with their request for judicial assistance.
Jeannette Balmer, spokeswoman for the Federal Prosecutor's Office, on Wednesday confirmed reports that the US had handed over the requested information at the beginning of September.
She added that the prosecutor's office was happy with the information provided, and expected to hand over the dossier to federal investigators within the next two months.
Washington's decision to comply comes after a prominent nuclear weapons expert, David Albright, told the US Congress last May that the Swiss investigation was stalled because the US had ignored repeated requests for judicial assistance.
The case centres around two brothers, currently in Swiss custody, who are suspected of helping to supply gas centrifuge parts for use in Libya's nuclear weapons programme between 2001 and 2003. Gas centrifuges are a vital element in the production of weapons-grade material.
One of the brothers, Urs Tinner, is said to have supervised the production of more than 2,000 centrifuge parts in Malaysia. A German-registered freighter carrying components from Malaysia to Libya was intercepted in autumn 2003.
Swiss authorities are investigating whether the brothers broke Swiss legislation on war materials by knowingly contributing to the production of nuclear weapons.
According to federal prosecutors, brothers Urs and Marco Tinner remain in custody. Their father Friedrich was released in January after almost five months in detention.
Washington's failure to respond to "multiple" Swiss appeals was revealed earlier this year by Albright, a former United Nations weapons inspector.
He told a US hearing into the nuclear trafficking ring run by Abdul Qadeer Khan, the father of Pakistan's atom bomb, that he found the lack of cooperation by the US "frankly embarrassing".
"It is difficult to understand the actions of the US government. Its lack of assistance needlessly complicates this important investigation," said Albright, who is president of the Washington-based Institute for Science and International Security.
He called on the US authorities to respond as quickly as possible, warning that the delay risked undercutting support for Swiss cooperation in non-proliferation matters.
There has been media speculation that Urs Tinner was working for the CIA.
In 2004 the International Atomic Energy Agency supplied the Swiss authorities with a list of two companies and 15 individuals suspected of dealing in nuclear material with Iran and Libya.
Swiss engineer Urs Tinner, who is suspected of helping Libya obtain nuclear weapons technology, was arrested in Germany in October 2004. He was extradited to Switzerland last year.
His father Friedrich and brother Marco were also arrested by the Swiss authorities on suspicion of breaking the law on war materials by illegally exporting nuclear bomb-making equipment to Libya.