BERN (Reuters) -The Swiss National Bank remains sceptical about buying bitcoins, Chairman Thomas Jordan said on Friday, despite calls from campaigners to change Swiss law and allow cyptocurrencies to be added to its currency reserves.

Buying bitcoin to add to the gold, foreign currencies, bonds and shares the SNB holds in its reserves was not without potential downsides like carbon emissions, Jordan said, pointing to the energy consumption of bitcoin mining and transactions.

"We have not yet decided that we want to invest in bitcoin. Actually for good reasons," he told the central bank's AGM.

"Currency reserves are international payments. They have to be liquid. They have to be sustainable. And we have to be able to sell and buy them."

A campaign group wants the SNB to hold part of its currency reserves in bitcoin, and to put the issue to a referendum.

It argues the move would help secure Swiss sovereignty and neutrality, as well as diversify the SNB's investments.

One of the campaigners, Luzius Meisser from crypto currency broker Bitcoin Suisse, said the SNB had made massive losses on its investments in government bonds of other countries when it could have made a big profit from buying bitcoin instead.

"I firmly believe that it would strengthen the Swiss franc and the independence of the Swiss National Bank if we spent less on loss-making government bonds and started holding bitcoin," Meisser told the meeting.

"Imagine you had the possibility to send something of value to your great-grandchildren in the year 2099. Would you prefer them to get 50,000 euros or a hard bitcoin? To me, the choice is clear."

(Reporting by John Revill, Editing by Friederike Heine)