Quoting 'reliable sources from Thailand' the ministry said in a statement on its website that Tamil Tiger arms procurement chief Kumaran Padmanadan, also known as "KP", has been arrested in Bangkok on Monday.
It gave no further details.
Kumaran Padmanadan has long been in charge of Tiger weapoins procurement and was believed to have been operating using false identities.
He has also been implicated in several assassinations of political leaders.
He was known to be living in Thailand and had been on the wanted list of the International Police (Interpol) for some time.
The Bangkok Post newspaper said Thailand has arrested the procurement and finance chief of the Tamil Tigers of Sri Lanka.
Pathmanadan apparently had obtained Thai citizenship, it said.
It was he who ran the global network of Tiger offices and its weapons procuremen