The Reserve Bank won't say whether it intervened in the currency markets on Thursday, after a British bank sold a large number of New Zealand dollars.
Following recent strong gains, the New Zealand currency fell more than a cent on Thursday to below 72 US cents.
Derek Rankin, of Rankin Treasury, says rumours emerged after a British bank sold a large amount of New Zealand dollars.
He says this, coupled with the Kiwi's recent strength, led some traders to believe that the Reserve Bank had intervened to bring the currency down.
Currency trading data to be released next month will confirm whether the central bank intervened.
The Reserve Bank last intervened in the currency markets in 2007 when the dollar was at 76 US cents.
While the Kiwi has been the strongest performer against the US dollar in Asia this year, currency experts say it is not yet at the level which would justify intervention.
At 7am on Friday the dollar was trading at 71.56 US cents.
