Glaxo Wellcome and SmithKline Beecham are to delay completion of their merger by one month.

The two firms were set to create the world's largest pharmaceutical group by 21 August. It has now been put back until 25 September.

The two companies are still awaiting regulatory approval from the US authorities, but remain optimistic that they will get the green light to merge.

"Whilst the regulatory process is taking slightly longer than anticipated, we continue to work diligently towards the earliest possible closure of the merger and we are confident that we achieve a positive outcome," a statement from the two companies said.

Demand for drugs

The merged group has three products which the US Federal Trade Commission wants them to sell.

These are SmithKline's anti-viral drugs Famvir and Vectavir as well the anti-nausea cancer medication Kytril.

"There are no particular difficulties with the FTC but this is a very involved process," SmithKline Beecham chief executive Jean-Pierre Garnier said.

Earlier, SmithKIine Beecham reported its final set of results before the merger.

Pre-tax profits rose 14% to �1.057bn a year earlier.

"I am pleased with SmithKline Beecham's strong performance ... it reflects SmithKline Beecham's continued momentum as we move towards the completion of our proposed merger with Glaxo Wellcome," Mr Garnier said.

Its profits were helped by strong sales of anti-depressant Paxil and antibiotic Augmentin as well as its newer anti-diabetes drug Avandia.

Shareholders at the two companies are expected to vote to approve the merger at an extraordinary general meeting on 31 July.

"Although not good for sentiment the delay of the merger by a month has little real impact. We would expect integration processes to already be under way as far as possible," analysts at UBS Warburg have said.