JAKARTA, May 8 (Reuters) - Copper concentrate export permits for Freeport Indonesia and Amman Mineral Nusa Tenggara will be extended, Indonesian President Joko Widodo told reporters on Wednesday, adding details for the extensions are still being calculated.

Freeport Indonesia and Amman are each building copper smelters, and both are expected to start operation in June. However, the companies have said it would take months to ramp up the capacity for the new smelters to be able to absorb their copper concentrate outputs.

The current permits are set to expire on May 31.

Widodo said the permits will be extended and the government was still calculating the details of the extension.

"I suppose with the completion of the smelters, it shows their strong desire to start downstreaming in the country," he said of the companies' plans, referencing his policy priority of having more mineral processing occur in Indonesia.

Freeport Indonesia and Amman did not immediately respond to a request for comment when asked about the permit extension.

Freeport is preparing to

ship as much

as 900,000 metric tons of copper concentrate starting in June from its Grasberg mine after positive talks with Indonesia to extend its export licence, two sources said earlier this week. (Reporting by Stanley Widianto, Fransiska Nangoy, and Bernadette Christina; Editing by John Mair)