BP is being investigated by US regulators over alleged manipulation of the gas market, dealing a blow to its attempts to rehabilitate its tarnished reputation following the Gulf of Mexico disaster.

The US Federal Energy Regulatory Commission (FERC) notified BP of its preliminary conclusions relating to the alleged manipulation in November, a footnote to BP's annual results revealed. "The FERC staff will determine whether to pursue the investigation, to close the investigation, or to seek authority to pursue resolution by settlement."

Another regulator, the US Commodity Futures Trading Commission (CFTC), also served BP with a notice of intent to recommend charges over similar alleged violations later the same month. They relate to trades made by several BP entities between October and November 2008 in Houston.

In a statement, BP said it had provided both agencies with a detailed response, saying that it "did not engage in any inappropriate or unlawful activity". It added that it has fully co-operated with the investigations and that its trading and transport operations comply with the law.

In a separate case in 2006, BP paid $300m (£188m) to settle charges that it had manipulated the US propane market.

The disclosure that BP is being investigated for a second time over alleged manipulation of the gas market in the US will raise questions about the company's zeal to change its practices.

Bob Dudley, who took over as chief executive from Tony Hayward after the Gulf disaster, pledged to put safety and risk management at the heart of the company's operations. Hayward promised when he replaced Lord Browne, who left soon after the Texas City refinery explosion and an Alaskan oil leak, to focus "like a laser" on safety.

Separately, the administrator of BP's $20bn (£12.3bn) Gulf spill compensation fund was accused by Mississippi's attorney general, Jim Hood, of "sweeping deficiencies and violations of law". He said the courts needed to intervene to force BP to fulfil its legal obligations.

White House appointee Kenneth Feinberg took over the fund from BP last summer. The statement filed with a federal court in Louisiana said: "Court intervention and action is needed to compel BP to cure its failure to provide a claims process that fulfils the requirements of the Oil Pollution Act of 1990, state law and prior public commitments of BP."

The prospects of BP reaching a quick settlement in its dispute with Russian joint venture TNK-BP over the British company's proposed new alliance with Kremlin-controlled rival Rosneft also dimmed today. Rosneft's chief financial officer, Peter O'Brien, said he "does not see" TNK-BP as a potential partner in the alliance.

"They have neither the technology, nor the experience, nor the personnel," he said. TNK-BP has secured an injunction preventing BP from completing the share swap with Rosneft and freezing negotiations, claiming that it contravenes its shareholder agreement requiring BP to offer the joint venture first refusal on any further business opportunities in Russia. The two sides are now preparing to begin arbitration proceedings. The comments jarred with Dudley's conciliatory remarks. Dudley hinted that it had always been BP's intention to offer TNK-BP some involvement in the Rosneft venture, without giving details, adding that he thought a "sensible business solution" to the dispute could be found.