MOSCOW, Dec 25 (Reuters) - The Russian rouble firmed to a one-week high in light trade on Friday, crossing the 90 mark against the euro with the help of higher oil prices and month-end taxes that usually prompt companies convert their foreign currency. At 0706 GMT, the rouble was 0.4% stronger against the dollar at 73.65, paring losses of the past week but trading still far away from levels of around 61 seen in early 2020 before the COVID-19 pandemic hit Russia. Against the euro, the rouble added 0.2% to 89.91 . The rouble regained ground this week thanks to demand related to local tax payments, but risks of new sanctions against Russia capped its recovery. The United States promised to retaliate over a massive hacking campaign that allegedly involved Russians. It is also urging European allies and private companies to halt work that could help build the Nord Stream 2 natural gas pipeline and is preparing wider sanctions on the Russian project in coming weeks. Russian stock indexes were mixed. The dollar-denominated RTS index rose 0.3% to 1,382.2 points. The rouble-based MOEX Russian index was 0.2% lower at 3,231.3 points, having hit an all-time high of 3,318.39 last week. For Russian equities guide see For Russian treasury bonds see