(Updates prices, adds FX interventions, OFZs, Locko-Invest) MOSCOW, Feb 3 (Reuters) - Rising oil prices helped the Russian rouble to firm on Wednesday after two successful treasury bond auctions, but gains were capped following the jailing of Kremlin critic Alexei Navalny. A Russian court on Tuesday handed Navalny a 3-1/2-year prison sentence, straining ties with the West. The rouble’s gains were limited even as oil prices climbed higher. It traded at around 63.5 to the dollar when oil prices last hovered near current levels in February 2020. By 1529 GMT, the rouble was up 0.3% against the dollar at 75.99 and had gained 0.5% to trade at 91.29 versus the euro. Brent crude oil, a global benchmark for Russia’s main export, was up 2% to $58.61 a barrel, a near one-year high. “There is another complication for the stock market and the rouble in the face of yet another case against one of the opposition politicians who European and U.S. embassies defend,” said Otkritie brokerage, without using Navalny’s name. Russia’s finance ministry said it would slash its foreign currency buying in February to 2.4 billion roubles ($31.6 million) worth of FX a day, a near three-fold decrease on the previous month.