By Andrey Ostroukh and Alexander Kolyandr 

MOSCOW--Russia's central bank surprised financial markets with a two-percentage point cut in its key interest rate Friday, sending the ruble lower even as the bank said the currency was showing signs of stabilization.

The bank had come under heavy pressure from industrialists and commercial bankers to lower the rate, which had been raised 6.5 points to 17% at an emergency meeting in December as the ruble was in free fall.

But with inflation continuing to rise and prices of oil, Russia's main export, still weak, the ruble has remained under pressure. Fears of further Western sanctions amid escalating violence in Ukraine have added to that pressure.

The White House pointed to the central bank's move as evidence of the negative economic impact on Russia of President Vladimir Putin's "expedition into eastern Ukraine."

"We're hopeful that as these cost mount, that it will prompt...President Putin to re-evaluate his strategy," White House press secretary Josh Earnest said.

Russia's Central Bank Chairwoman Elvira Nabiullina said Friday's move--the first easing after six rate increases last year--was aimed at "balancing the goals of subduing inflation and restoring economic growth."

Describing the December increase as "an emergency measure," she noted that the new rate of 15% was still "rather high."

When it announced the rate cut, the central bank said that a sharp economic contraction would ease inflationary pressures later this year.

But many investors said the unexpected cut seemed to send a worrisome signal about the central bank's ability to withstand pressure from the Kremlin and powerful domestic interests to boost growth with easier money, even at the expense of rising inflation and pressure on the currency.

The ruble fell beyond 72 per dollar after the announcement, its lowest level since December.

Concerns about central-bank independence were heightened earlier this month when Ms. Nabiullina replaced her monetary policy chief, economist Kseniya Yudaeva, with a banking-industry veteran, Dmitry Tulin. Ms. Yudaeva, long-considered a close ally of Ms. Nabiullina, was given responsibility only for analysis and forecasting.

Officials denied the move undermined the bank's independence, but in recent weeks, even top cabinet members have criticized the bank for what one called a "maniacal" devotion to the principle.

"There is lack of consistency...and complete unpredictability in their actions, which isn't good for the markets," said Dmitry Petrov, an economist at Nomura, said of the bank. "We don't know whether it has been the pressure or change in the governance that resulted in this shift, but it may prove very costly in terms of their ability to achieve inflation targets," he added.

Mr. Petrov also warned the move could raise fears of capital controls, something the government has so far ruled out.

Russian government officials welcomed the easing. Finance Minister Anton Siluanov, who criticized the central bank for being slow with monetary tightening late last year, said that the rate cut was "absolutely correct and balanced," adding that the "exchange rate has reached equilibrium."

In her comments, Ms. Nabiullina also suggested the bank was working together with the government, which this week approved a 2.34-trillion-ruble ($33.9 billion) program to ease the effects of the economic crisis. Ms. Nabiullina said the rate cut was aimed at restarting lending to industry, "which is one of the goals of the anticrisis plan."

In its rate-cut statement, the central bank said that while inflation--now running at 13.1%--was likely to continue to rise in the coming months, the deepening slowdown in the economy would bring down price growth later in the year. However, inflation won't fall below 10% until January 2016, the bank said.

The central bank warned that Russia's economy faced a "substantial contraction in output," because of the drop in oil prices and Western sanctions, which have led to "the closure of external financial markets for Russian borrowers."

It warned that investment would decline, while falling real incomes and tightening consumer credit would "reduce consumer activity." The central bank forecast that the Russian economy would contract by 3.2% in the first half of this year, compared with growth of 0.6% during the whole of 2014.

The central bank has come under intense pressure in recent weeks from industry and commercial banks to lower rates. Even President Putin offered only mixed support for the central bank's handling of the ruble crisis, saying some of its moves were belated.

The central bank didn't immediately respond to a request for comment on allegations that its independence had been compromised.

Economists said the ruble could face further pressure in the coming weeks if other credit-rating firms join Standard & Poor's, which downgraded Russia to 'junk' level earlier this month. With violence in Ukraine continuing to rise, pressure for more Western sanctions could also hurt the currency.

"The ruble is still vulnerable in the current environment, but perhaps the [central bank] judged that the base rate at 15% should provide sufficient insulation for the ruble," said Piotr Matys, a rates strategist at Rabobank.

Chiara Albanese in London contributed to this article.

Write to Andrey Ostroukh at andrey.ostroukh@wsj.com and Alexander Kolyandr at Alexander.Kolyandr@wsj.com

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