LONDON, Aug 3 (Reuters) - British Airways posted a 28 percent rise in quarterly operating profit on Friday to beat analysts' forecasts, but warned a weak dollar and soaring fuel prices would slow full-year revenue growth and raise costs.

Earnings before interest and taxes for the three months to end-June rose to 263 million pounds ($534 million), BA said in a statement to the London Stock Exchange.

That beat the average forecast of 224.5 million pounds from a poll of four analysts from Reuters Estimates, whose forecasts ranged from 206 million to 237 million pounds.

Europe's third-largest airline said a consortium it belongs to that includes U.S. private equity firm TPG was working on due diligence of Spanish airline Iberia.

BA said its operating margin rose to 12 percent versus 9.2 percent in the same period a year earlier. It reiterated a target of 10 percent for the full year.

"Profits are up as a result of the steps we took last year to control costs and strengthen our business," said Chief Executive Willie Walsh.

Profit before tax rose to 289 million pounds from 191 million.

"Revenue is flat before exchange and reflects the continued impact of security and baggage restrictions on shorthaul and premium transfer traffic, which Heathrow has been struggling to cope with," Walsh said, referring to London's biggest airport.

BA softened its revenue growth guidance by 1 percentage point to around 4 percent, citing the continued weakness of the U.S. dollar.

It also said rising fuel costs would take a bite, rising by 120 million pounds this year, 20 million worse than earlier forecast.

BA set aside a 350 million pound provision in May for fines stemming from price fixing on fuel surcharges and announced the bulk of the fines this week.

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