The country's foreign exchange reserves declined by $1.265 billion to $400.52 billion in the week to September 28 due to a fall in foreign currency assets, according to RBI data.
In the previous week, the reserves had risen by $1.3 billion to $401.790 billion.
In the reporting week, foreign currency assets, a major component of the overall reserves, declined by $1.169 billion to $376.243 billion, as per the data.
Expressed in US dollar terms, foreign currency assets include the effect of appreciation or depreciation of the non-US currencies such as the euro, pound and yen held in the reserves.
Forex reserves had touched a record high of $426.028 billion in the week to April 13, 2018, but have been declining since then.
Gold reserves dipped by $70.7 million to $20.343 billion in the reporting week.
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The special drawing rights with the International Monetary Fund (IMF) declined by $10.4 million to $1.470 billion.
The country's reserve position with the IMF also dipped by $14.6 million to $2.468 billion, the apex bank said.