Collapsed hedge fund Amaranth Advisors LLC and its former chief energy trader — who is attempting to set up a new company in Alberta — were accused by U.S. officials Wednesday of trying to manipulate natural gas markets in 2006.

The Commodity Futures Trading Commission filed a civil complaint in federal court against Amaranth and trader Brian Hunter, focusing on the rapid sale of March and May futures contracts just as they were about to expire and an alleged attempt to cover up those actions.

Amaranth, which was based in Greenwich, Conn., folded in 2006 after losing some $6 billion US.

Hunter's lawyer issued an e-mail statement denying his client had tried to manipulate the market.

"Brian Hunter simply did not undertake any manipulative trading and we are going to prove it," lawyer Michael Kim said in a statement.

Geoffrey Aranow, a lawyer for Amaranth's former CEO Nick Maonis, said in a statement that "there is no evidence here of any intent to manipulate the markets."

Earlier in the week, Hunter sought a restraining order against the U.S. Federal Energy Regulatory Commission, arguing that the agency exceeded its power by trying to bring an enforcement action against him.

Hunter is starting a new hedge fund based in Calgary called Solengo Capital Advisors. His lawyers wrote in a court complaint that government action will "irreversibly damage both [Hunter's] personal reputation and the viability of Solengo, such that Solengo will cease to exist."

The government's complaint alleges that Amaranth, in February and April of 2006, tried to lower natural gas prices on the New York Mercantile Exchange to benefit trading positions it held on the InterContinental Exchange Inc., an electronic futures exchange.

The complaint quotes colourful instant-message exchanges between Hunter, Amaranth employees and traders at other companies.

In one instant message in February 2006, Hunter wrote "shhhh" to a natural gas trader at another firm about Amaranth's plans to sell thousands of natural gas contracts.

The agency also alleged Amaranth made false statements in a letter to Nymex officials in August 2006 and accused the hedge fund of trying "to cover up what actually occurred."

Hunter earned more than $100 million in 2005, said the complaint, which seeks to bar Hunter and now-defunct Amaranth from trading commodities in U.S. markets.

"He presumably thought that his illegal activity would go undetected," said Gregory Mocek, the CFTC's director of enforcement, in a conference call with reporters. "He was wrong."

Mocek said the agency was not able to determine that Amaranth had been successful in actually affecting prices.

In his statement, Hunter's lawyer said Kim called the CFTC's action "politically motivated," coming weeks after U.S. senators criticized the agency in hearings. Mocek, who said the agency's investigation started in the summer of 2006, denied there was any political influence.

In June, Senate investigators alleged that Amaranth's trades inflated natural gas prices and helped to drive up heating bills last winter. The report found that Amaranth engaged in "excessive speculation," but did not allege market manipulation.

To avoid trading limits it faced on the Nymex, Amaranth shifted its activity to ICE, an Atlanta-based exchange that is free from limits on trading, the report found. Senators have called for more oversight of ICE and other such exchanges.