Pharmaceutical giants Glaxo Wellcome and SmithKline Beecham have been forced to delay their planned merger.
The brakes were applied after US regulatory authorities said they wanted more information about the deal.
The two firms had hoped to start trading as GlaxoSmithKline on September 25 but said completion of the merger would now only occur at the end of the year.
The delay is the result of the US Federal Trade Commission asking for more information about anti-smoking products being developed by the two firms - including Glaxo's Zyban product and SmithKline's Nicorette and Nicoderm products - amid concerns a merged company could dominate the US market for such products.
The companies were due to attend a High Court hearing on September 21 as the last stage in the merger process, which is also now likely to be postponed as clearance from the US has not been received.
Sir Richard Sykes and Jean-Pierre Garnier, chairman-elect and chief executive-elect respectively of the new company, said they remained confident the merger would proceed.
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