The Federal Reserve’s custody holdings of Treasuries fell for the first time in a month at a time Japan was likely intervening to support its currency, with markets debating whether the nation offloaded US securities to fund its yen purchases.

The amount of marketable US Treasury securities the Fed holds for foreign official and international accounts slipped by $8.7 billion to $2.73 trillion in the week to May 6, according to data released by the central bank. Japan’s Ministry of Finance was estimated to have spent about $54.7 billion to buy its currency during the same period. The drop in the Fed’s holdings is consistent with the possibility that Japan’s intervention involved Treasury sales.