U.S. Attorney Preet Bharara (buh-RAH'-ruh) says the millions of leaked documents known as the Panama Papers are "relevant" to a criminal investigation his office has opened.

Bharara sent a letter to the International Consortium of Investigative Journalists asking to discuss the papers, which focus on the offshore accounts of people and companies. They were leaked from the Mossack Fonseca & Co. law firm.

The consortium oversaw an effort from investigative reporters around the world to delve into the documents, which show how the world's richest use shell companies and other tactics to avoid tax obligations.

Bharara's office didn't comment. The consortium confirmed it received the letter, but had no comment on any response.

The documents have set off a global firestorm and brought concerns around tax evasion to the fore.