By Carla Mozee, MarketWatch

LONDON (MarketWatch) -- U.K. stocks fell for the first time in four days on Friday, with a drop in mining shares yanking the FTSE 100 into red territory.

The benchmark index fell 0.4% to close at 6,844.51, paring its weekly gain to 0.4%. It rose 1% for May, during which it reached its best closing level since 1999.

Miners were ranked among the session's sharpest decliners, as iron-ore prices slumped and the metal looked set to log its sixth monthly loss for a record run of declines. With iron ore below $96 per ton, the move "will make some names in the resource sector unhappy," wrote Scott Schuberg, chief executive at Australia-based Rivkin Securities, in a note Friday.

Anglo American PLC shares slid 5.7%, their heaviest fall in nearly two months. Rio Tinto PLC fell 4.1% and BHP Billiton PLC (BHP) lost 3.7%. Silver and gold producer Fresnillo PLC gave up 3.5%.

But Smith & Nephew PLC shares were again among top performers in the FTSE 100 as they rose 1.7%. The shares have jumped nearly 10% since Wednesday on speculation that the artificial-joint maker will land an acquisition bid. Medical-device maker Stryker Corp.'s (SYK) chief told Fox Business on Thursday that his company had worked on a possible bid for its U.S. rival, but a formal offer hasn't materialized.

Meanwhile, consumer confidence in the U.K. hit a nine-year high, according to polling firm GfK, highlighting the view that the British economy continues to improve.

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