All but two of the blue-chip index's sectors ended in the red as it shed 0.5pc - its biggest intraday fall in nearly two weeks, while the mid-cap FTSE 250 lost 0.4pc.
Among major drags on the main index were oil heavyweights Shell and BP, which tracked a slump in crude prices amid expectation that output would rise in the Gulf of Mexico following last week's hurricane, as well as miners .
Bright spots on the index were tobacco giants British American Tobacco and Imperial Brands after US peer Philip Morris reported its sixth consecutive quarter of profit beat. BAT surged 6.1pc on its best day in over a decade while Imperial Brands added 2.2pc.
Slug and Lettuce owner Stonegate Pub Company agreed to buy Ei Group for 285 pence a share, a 38pc premium to Wednesday's close, which sent the mid-cap pub chain's stock to its highest in more than a decade.
The stock surged nearly 39pc and helped fellow mid-cap pub operators Mitchells & Butlers, Greene King, J D Wetherspoon and Marston's rise between 1.3pc and 4.2pc.
TRADE WAR IMPACT
Meanwhile, the effects of a protracted China-US trade dispute on corporate earnings and worries that trade tensions could further escalate have turned investors across the globe risk-averse.
Sentiment weakened as US railroad operator CSX and German tech heavyweight SAP flagged an impact from the trade war and and a report that progress towards a trade deal had stalled weighed on sentiment.
After a slump in May due to rising worries that Washington's trade war with China and other partners would escalate, the FTSE 100 has steadied and is on course for its best year since 2016.
The exporter-heavy index's gains have been fuelled by hopes of interest rate cuts by central banks and the plummeting value of the pound due to concerns around the Conservative leadership election and risks from Brexit.
AIM-listed ASOS tanked 23.2pc to its lowest in 4-1/2 years after it blamed operational issues for its third profit warning in eight months.
Its shares also weathered their worst one-day drop since December, when the online fashion retailer's previous warning had triggered a global retail sell-off.
Luxury brand Burberry, which is on course for its best week in more than a decade after posting robust sales growth on Tuesday, gave up 1pc.
Budget airline easyJet gained 3.4pc on the midcap index after it stood by its annual profit forecast, reassuring investors despite softening demand in the industry due to Brexit-driven consumer uncertainty.