It doesn't just rain at BP these days, it pours, and on top of a row with Russian partners that's delayed its venture with Rosneft, the UK oil giant today stands accused of manipulating the US gas market.The US Federal Energy Regulatory Commission (FERC) and the US Commodity Futures Trading Commission (CFTC) are investigating "several BP entities" as part of a probe into trading in the next-day natural gas market at Houston Ship Channel in October and November 2008.Although BP maintains it has not been part of any "inappropriate or unlawful activity", the FERC still hasn't made its mind up whether to prosecute or not.BP paid about $300m in 2006 to settle charges of propane market manipulation.The news comes a day after the firm's plans for an $8bn Arctic exploration deal with Kremlin-backed Rosneft stalled following a High Court decision to grant an injunction to freeze the deal following a request from BP's Russian partners at TNK-BP.A London court heard an action launched by Alfa-Access-Renova (AAR), the vehicle owned by a number of Russian oligarchs and which has a 50% stake in TNK-BP. They want to stop the deal with state-run Rosneft, agreed on 14 January, claiming it breaches terms of their own joint venture with the UK firm that includes a clause giving them the right to be part of any action on Russian soil.