Portugal's finance ministry says it is looking at ways of preventing government departments from using tax havens after the Treasury debt agency was found to have held an investment in Jersey.

The Finance Ministry says that the agency held 133 million euros ($149 million) of bonds in a Jersey-based company last year.

It said in a statement Friday the bonds resulted from a financial operation involving Portugal's state-owned rail company. The bonds matured last July.

The statement said the government is studying the adoption of new procedures ensuring no public institutions have investments in offshore tax havens.

Tax evasion became a prominent political issue following a leak of documents from a Panama-based law firm last month.