Malaysia has arrested a Sri Lankan businessman who is accused of acting as the chief financial officer in a Pakistani-led global nuclear weapons smuggling ring.

Malaysian authorities say Buhary Syed Abu Tahir is in custody as a threat to national security. The officials did not specify charges against Mr. Tahir, or why they had decided to arrest him now.

In February, Malaysian police questioned Mr. Tahir but did not charge him. In a subsequent report, the police say he confessed to the role of middleman in a worldwide nuclear weapons black market operation.

The report said Mr. Tahir admitted to being a go-between for the leader of the black market operation, Abdul Qadeer Khan. Mr. Khan headed the creation of Pakistan's atomic weapons program.

Earlier this year, President Bush described Mr. Tahir as the ring's "chief financial officer and money launderer."

In his reported confession, Mr. Tahir said he had assisted Mr. Khan in the sale of Pakistani centrifuges - used in making nuclear weapons material - to Iran in exchange for $3 million.

According to the police report, the deal was made in the 1990s and was transacted through the ring's headquarters in Dubai.

He also said Mr. Khan had later sold enriched uranium to Libya.

Mr. Khan has already confessed to trafficking in nuclear materials, but has been pardoned by the Pakistani government.