By Sara Sjolin, MarketWatch

LONDON (MarketWatch) -- U.K. stocks moved lower on Friday, with Petrofac posting its biggest loss since November after warning 2014 earnings will be lower than expected.

The FTSE 100 index dropped 0.4% to close at 6,814.57, sending the benchmark 0.1% lower for the week.

Topping the list of losers, shares of Petrofac Ltd. tumbled 15% after the oil-services firm said it expects profit for 2014 to be between $580 million and $600 million, lower than the $650 million reported in 2013. The warning was mainly due to lower than expected earnings from its Integrated Energy Services, or IES, business.

Shares of International Consolidated Airlines Group SA (ICAGY) gave up 4.8% after the company said it narrowed its loss in the first quarter, although performance at discount unit Vueling -- which posted a 30 million euro ($41 million) loss -- was slightly disappointing. IAG is also the owner of British Airways.

Also on the decline in London, shares of Rolls-Royce Holdings PLC shaved off 1.2% after Barclays cut the engine maker to underweight from overweight. The analysts said expectations of slow growth over the next two years, significant cash and margin headwinds, accounting concerns and questions over capital allocation led to the downgrade.

On a more upbeat note, shares of Intertek Group PLC rose 1.4% after Credit Suisse lifted the product-testing firm to outperform from neutral.

Investors in London largely ignored the latest on the data front. The Office for National Statistics said manufacturing output rose 1.4% in January to March, the fastest quarterly pace of growth since the third quarter of 1999.

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