By Andrey Ostroukh

MOSCOW--Russia's finance ministry is proposing to increase the use of its reserve fund this year, spending more than three quarters of the budget coffers by the end of 2015, Finance Minister Anton Siluanov said on Wednesday.

As Russia's revenue falls along with oil prices, and Western sanctions have cut the country off from international financing, the finance ministry will tap the reserve fund for the first time since 2009.

To support its oil-dependent budget, Russia will spend around 3.7 trillion rubles ($595.2 million) from the reserve fund, money that the government put aside during the years when oil prices were high, Mr. Siluanov said. This will bring the size of the fund to around RUB1.7 trillion by the end of the year, Mr. Siluanov said. The reserve fund stood at RUB4.72 trillion as of March 1.

Last week, a senior finance ministry official said estimated spending from the fund stood at RUB3.2 trillion this year, far above original expectations of RUB500 billion.

Dipping into the reserve fund will also further drain Russia's international reserves, of which the fund is a component. Reserves slipped below $365 billion for the first time since 2009 this week.

The risk of a rapid depletion of Russia's reserves was one of the key reasons behind a decision by Moody's Investors Service Inc. to downgrade the country's sovereign credit rating to junk in February.

Write to Andrey Ostroukh at andrey.ostroukh@wsj.com