By Sara Sjolin, MarketWatch

LONDON (MarketWatch) — The U.K.’s FTSE 100 index ended slightly lower on Tuesday, as miners added pressure after iron-ore prices declined, offsetting optimism over a growth upgrade from the International Monetary Fund.

The benchmark index /quotes/zigman/3173262/realtime UK:UKX -0.04%  closed a bit lower at 6,834.26, after swinging between small gains and losses earlier in the day.

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The IMF lifted the economic growth forecast for the U.K. for 2014 to 2.4% from an earlier estimate of 1.9%, saying activity in the country has been buoyed by easier credit conditions and increased confidence.

The move wasn’t, however, enough to send the FTSE 100 rallying, with mining firms declining as iron-ore prices fell to their lowest level in six months. The downturn was partly due to a retreat by Chinese buyers in response to slowing domestic steel production and rising stockpiles. Shares of Rio Tinto PLC /quotes/zigman/155899/realtime UK:RIO -3.13%   /quotes/zigman/176317/realtime AU:RIO -1.66%   /quotes/zigman/182541/delayed/quotes/nls/rio RIO -3.20%  dropped 3.1%, Anglo American PLC /quotes/zigman/470624/realtime UK:AAL -2.66%  lost 2.7%, BHP Billiton PLC /quotes/zigman/184879/realtime UK:BLT -1.70%   /quotes/zigman/270355/delayed/quotes/nls/bhp BHP -1.12%   /quotes/zigman/180893/realtime AU:BHP -1.49%  fell 1.7% and Glencore Xstrata PLC /quotes/zigman/5131911/realtime UK:GLEN -1.27%  gave up 1.3%. Metals prices were mixed.

On a more upbeat note in London, shares of Unilever PLC /quotes/zigman/409909/realtime UK:ULVR +1.76%   /quotes/zigman/203077/delayed/quotes/nls/ul UL +3.26% , the maker of Dove soap and Axe deodorant, gained 1.8% after the consumer-products company reported a rise in full-year earnings.

“Unilever’s results were refreshingly dull, doubly so in view of the amount of second-guessing by analysts and investors over the last couple of weeks. EPS came in 3% ahead of our forecast at €1.58, and we can’t see anything untoward in their composition,” said James Edwardes Jones, an analyst at RBC Capital Markets, in a note.

Melrose Industries PLC /quotes/zigman/12942685/realtime UK:MRO +0.64%  gained 0.6% after the investment company said it will return £600 million to shareholders following recent disposals of businesses.

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