Catching market players offguard, the country's foreign reserves rose by $5 billion last week, their first reported gain since the crisis took off in late September.

The reserves stood at $454.9 billion on Nov. 28, the Central Bank said, up from $449.9 billion Nov. 21, following a $3.6 billion loss the week previous.

The reports from the past two weeks signal a departure from the $12 billion to $15 billion weekly losses the reserves suffered this fall, something Prime Minister Vladimir Putin seemed anxious to stress in his televised question-and-answer session. The prime minister highlighted that the reserves had increased "for the first time in recent weeks."

The $5 billion growth is "surprising" because of the large amount of money the Central Bank has spent on defending the ruble, said Yelena Rybakova, Citibank's chief economist in Moscow.

Last week alone the bank is estimated to have sold $2 billion to $6.5 billion worth of foreign currency as low crude oil prices put greater pressure on the ruble.

Last month, the Central Bank widened the ruble's trading band against a dollar/euro basket three times, each time by a total of 10 kopeks on either side. The moves were widely criticized, with many analysts saying a gradual weakening would put downward pressure on the ruble and quickly burn through the country's foreign currency reserves.

Although the increase came as a surprise, analysts seemed doubtful that the gains would continue.

"A week doesn't make a trend," said Ronald Smith, chief strategist at Alfa Bank.

Citibank said the jump in the reserves was likely because of the stabilization fund's $14 billion, or 5.9 percent, gain for the month of November, which the Finance Ministry announced Monday.

While the link between the stabilization fund's and foreign reserves' gains was unclear, under the circumstances it appeared the most reasonable explanation, Rybakova said.

"There's a small valuation effect, but I don't think that could account for such a large increase during the last week," she said.

According to Citibank estimates, by the euro and pound appreciation against the dollar likely accounted for up to $3.5 billion of the reserves' appreciation. Other factors could be the significant appreciation of securities last week and a shift in Russia's import-to-export ratio.

"This may be an indication that imports are falling sharply," since a sharp drop in imports increases the demand for foreign currencies, Smith said. Data for this period's imports will not be released until January or February.

Rybokova said that as long the state continued to defend the ruble the country would continue to lose reserves.

And based on this week's falling oil prices, the amount that the Central Bank will burn through is likely to increase, said Smith of Alfa Bank.

"In my view, [this week's gain] does not change the bottom line, which is that the ruble is overvalued and that it needs to adjust in line with market fundamentals," Rybokova said.

"Until then, the trend of losing reserves will continue."