By Andrey Ostroukh 

MOSCOW--Renewed concerns about a fresh round of Western sanctions against Russia pressured the already battered ruble Monday.

A surge in fighting in eastern Ukraine, which killed around 30 civilians in the Kiev-controlled town of Mariupol over the weekend, prompted U.S. and European leaders to threaten new sanctions against Moscow. The threat crowns a wide range of factors that have already hit the Russian currency.

By 0930 GMT, the ruble had fallen 2.1% to 65.6 against the dollar and shed 2.4% to 73.8 versus the euro, while the price of Brent crude had also declined 2%.

The ruble came under pressure as the market was cutting exposure to Russia-related risks on the back of deterioration of an already shaky situation in Ukraine, said Igor Akinshin, a trader at Alfa Bank in Moscow.

"We see a rather strong ditching of Russian risks on the back of deterioration of an already shaky situation in Ukraine," said Igor Akinshin, a trader at Alfa Bank in Moscow.

Although it isn't clear when any new sanctions against Russia could materialize, Western penalties have so far proved to have a clearly negative impact on Russia, along with massive capital flight last year. This year, the sanctions, which cut off Russian banks and companies from global capital markets, are widely expected to push the commodity-dependent economy into contraction for the first time since 2009.

The Bank of Russia has been actively supplying the market with foreign currencies after a domestic deficit of dollars and euros steered the ruble to record lows in mid-December. But the central bank's activity wasn't enough to ease concerns about state-driven demand for hard currencies at times of restricted access to the international debt market.

Later Monday, the country's No. 1 oil producer Rosneft is expected to raise up to 400 billion rubles ($6.1 billion) by selling bonds. The move follows a similar one in mid-December, when Rosneft raised 625 billion rubles just one day, fueling concerns that it would use the proceeds to buy foreign currencies just a day before the ruble crashed to its weakest ever level of 80.1 against the dollar. Rosneft denied that bought foreign currencies with the proceeds.

The ruble, which has lost more than 10% against the dollar so far this year, also remained under pressure amid concerns that Standard & Poor's will cut Russia's sovereign rating to junk. Although such expectations have been in place over the past few weeks, an actual downgrade will only add to the negative sentiment. The rating decision is expected by the end of this month.

The local tax payment period may ease pressure on the ruble as companies have to pay around 550 billion rubles by the end of the day, according to ING Bank estimates. Tax payments usually prompt export-focused companies to convert part of their dollar and euro revenues to meet local liabilities.

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