MOSCOW-The Russian ruble fell to fresh record lows against the euro-dollar basket on Friday, prompting central bank intervention to brake the currency's slide.

Pressured by massive capital flight on the back of Western sanctions over the Ukraine crisis, the ruble has been recently hit by sliding oil prices which are heading toward $90 per barrel. Local demand for foreign currencies needed to repay foreign debt also add to the downside pressure on the currency.

At 0900 GMT, the ruble traded at 44.46 versus the euro-dollar currency basket, the central bank's main gauge of the forex market, losing 0.4% on the day. The level suggests that the central bank has shifted the ruble's trading band twice on Friday, slowly retreating as it sells foreign currencies from reserves.

The central bank keeps the ruble within a floating band against the basket and intervenes when the ruble reaches the upper boundary of the band. According to the intervention rules, the central bank is set to shift the trading band higher by 5 kopecks after selling $350 million. Currently, the ruble's trading level suggests that the nine-ruble-wide trading band stands at 35.50-44.50. The central bank disclose the trading band location with a day lag.

The central bank intervened in the market this week for the first time since May but in a modest way. The data showed Friday that on October 1 the central bank sold just around $4 million when the ruble touched the band's upper boundary which then stood at 44.40 rubles per basket.

"A decline in oil prices, worrying news from Donetsk, Ukraine, and fears of further sanctions all put additional pressure on the ruble," Natalia Orlova, chief economist at Alfa Bank, said in a research note.

Versus the dollar, the ruble traded at 39.73, close to its all-time low of 39.89 hit on the last day of September. Against the euro, the ruble hovered at 50.17 beyond a psychologically important level of 50.

"The only positive observation at the moment is that the market is moving at very modest volumes, which indicates that ruble depreciation is more an issue of poor foreign currency supply than a sign of considerably strong demand," Ms. Orlova said.

Alfa Bank expects the ruble to recover to 37 rubles per dollar by the end of the year if oil prices stabilize at current levels. On Friday, Brent crude prices rose to $94.5 per barrel after falling as low as $92.19 overnight. Russia's 2014 budget envisages an average oil price of $103 per barrel.

Pressure on the ruble may last further as, with access to foreign debt markets curtailed by Western sanctions, Russian banks, companies and municipalities need to cover some $50 billion of foreign debt redemptions in the final three months of the year, according to the central bank.

However the central bank may feed the market with dollars and euros through a new tool announced by its chairwoman Elvira Nabiullina on Thursday. She said that the central bank would soon launch a forex repo--an auction in which the central bank provides liquidity for the market in foreign currencies--in one and four weeks.

"The announcement of FX swap operations by the central bank might offer support to the ruble. However, the exchange market is apparently not ready to trade on expectations. Therefore, we also prefer to wait for the regulator to take action", VTB Capital said in a note.

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