A longtime weight was lifted from the shoulders of Imperial Tobacco after the merger of US tobacco giants Lorillard and Reynolds American was given the green light by US anti-trust regulators after months of uncertainty, allowing the London-listed group to go ahead with its $7bn asset purchase from the merging pair.The deal, which still must clear some smaller legal hurdles, is expected to complete within weeks.The US Federal Trade Commission (FTC) has finally given the green light to a tie-up between Reynolds American and Lorillard as the deal was contingent on divestment of several brands and assets to Imperial in order to satisfy competition conditions.Imperial will become the new number-three player in the $100bn US market, with a 10% market share behind that of leader Altria Group's 47% and the new Reynolds-Lorillard combine's 34%."The announcement puts an end over 10 months of uncertainty about whether the deal would be signed off," said Mike van Dulken at Accendo Markets.Shares in Imperial were trading back up towards all-time highs at around 3,333p at 09:00 on Wednesday.