* Geopolitical concerns in the spotlight again * Rouble falls after nearing 4-month peak vs dollar * Rouble nears 74 vs dollar, 90 vs euro * MOEX down from all-time high (Adds rouble drop, quotes, background) MOSCOW, Dec 14 (Reuters) - The Russian rouble weakened swiftly in late trade on Monday, retreating from four-month highs versus the dollar on increased geopolitical concerns, sending the benchmark MOEX stock index down from a fresh record high. The rouble has been paring losses since the U.S. presidential election in early November and faces strong headwinds from market concerns about the possibility of new sanctions against Moscow. Reports that hackers believed to be working for Russia have been monitoring internal email traffic at the U.S. Treasury and Commerce departments have added to such fears. Russia denied any wrongdoing. The rouble slumped 1.4% to 73.94 versus the dollar as of 1827 GMT after touching 72.79, its strongest since Aug. 17. “We think the rouble could weaken to USD/RUB 74 if the geopolitical tension worsens,” Sberbank CIB said. Kremlin critic Alexei Navalny also reminded the market of possible new sanctions that pressured the rouble in the past few months. A joint media investigation said it had identified a team of assassins from Russia’s FSB security service as Navalny’s would-be killers, who had stalked him for years. The rouble’s weakness in the second half of 2020 has filtered into consumer prices, which is likely to prevent the central bank from cutting rates this Friday, a Reuters poll showed. If oil stabilises near current prices in the next 12 months, the rouble’s fair value would be at 71 versus the dollar, Raiffeisen Bank analysts said. Brent crude oil, a global benchmark for Russia’s main export, was up 0.3% at $50.11 a barrel, buoyed by hopes that a rollout of coronavirus vaccines will lift global fuel demand. Against the euro, the rouble fell 1.7% to 89.87 , trading far away from levels of around 70 seen in early 2020. On the stock market, the rouble-based MOEX Russian index was 0.7% lower at 3,254.8 points, having hit an all-time high of 3,314.20 earlier in the day. The dollar-denominated RTS index slid 1% to 1,398.1 points after climbing to 1,432.73, its highest since late February. For Russian equities guide see For Russian treasury bonds see (Reporting by Andrey Ostroukh; Editing by Giles Elgood and Richard Chang)