The country's foreign exchange reserves declined by $613.9 million to $393.12 billion in the week to December 14, on account of a fall in foreign currency assets, according to the RBI data.
In the previous week, the reserves had increased by $16.6 million to $393.734 billion.
In the reporting week, foreign currency assets, a major component of the overall reserves, dropped by $631.6 million to $367.865 billion.
Expressed in US dollars, foreign currency assets include the effect of appreciation or depreciation of non-US currencies such as the euro, pound and yen held in the reserves.
The reserves had touched a record high of $426.028 billion in the week to April 13, 2018. Since then, the forex kitty has been on a slide and is now down by over $31 billion.
Gold reserves rose by $37.2 million to $21.187 billion in the reporting week, the data showed.
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The special drawing rights with the International Monetary Fund (IMF) dipped by $7 million to $1.45 billion.
The country's reserve position with the IMF also decline by $12.5 million to $2.617 billion, the apex bank said.