Gains in Brent crude oil prices earlier today went into reverse, with oil hitting $49.17 per barrel.
Prices initially strengthened after four Arab countries cut ties with Qatar over alleged support of terrorist groups, but subsequently fell on fears the diplomatic rift could put OPEC cuts under threat.
The Maldives became the latest country to cut diplomatic ties today and contributed to a 7.3% drop when Qatar's stock market closed on Monday.
In the UK, the blue-chip index continued to underperform as miners and airline stocks remained weak.
Antofagasta (ANTO) and BHP Billiton (BLT) ticked 3.5% and 1.7% lower to 776.5p and £11.65 as forecast cuts from HSBC took its toll.
The potential impact on tourism from the London terror attacks on Saturday evening, higher oil prices and concerns over an extended laptop ban hit airline stocks.
The cocktail of bad news dragged on the performance of easyJet (EZJ) and British Airways owner International Consolidated Airlines (IAG).
These stocks fell 2.4% and 2.5% respectively.
P&O cruise operator Carnival (CCL) was also among the top fallers as the stock fell 1.6% to £50.50.
Legoland owner Merlin Entertainments (MERL) slid 2.4% to 524p as the market felt tourists would be less likely to visit its attractions.
In the UK, service sector growth was disappointing as Markit's Purchasing Managers' Index fell from 55.8 in April to 53.8 in May. The drop reflected a softer pace of new order growth as people tightened their pockets following further inflation.
Copper and gold were broadly unmoved at $5,621 per tonne and $1,279 per ounce.
On Wall Street, investor sentiment was subdued as the S&P 500 was flat at 2,427.
In Asia, stock markets closed in the red on Monday and China's SSE Composite took the biggest hit of 0.4% to 3,091.
FTSE 100 RISERS AND FALLERS
It was a good start to the week for Royal Mail (RMG) after announcing it exchanged conditional contracts for the sale of two of its plots on the Nine Elms site to Greystar for £101m in cash. Shares in the UK parcels deliver firm nudged higher to 440p.
In its latest deal, telecoms giant Vodafone (VOD) sealed a joint partner market agreement with LG UPlus for South Korea, but this failed to move the stock much at 230.3p.
The market reacted to results from AstraZeneca's (AZN) Phase III OlympiAD trial as its shares were 0.4% lower at £53.43. The pharma giant revealed patients showed a statistically-significant improvement in progression-free survival when using Lynparza (olaparib) tablets.
FTSE 250 RISERS AND FALLERS
Investors were optimistic about online food retailer Ocado (OCDO) after the company announced a long-awaited new international deal. Ocado confirmed an agreement with a regional European retailer to use its platform, which pushed the stock 1.1% lower to 312.3p.
Hungarian low-cost airline Wizz Air (WIZZ) increased its load factor - the percentage of available seats on scheduled flights occupied by passengers - from 90.1% in May 2016 to 91.1% in May 2017.
SMALL CAP RISERS AND FALLERS
Nearly two-fifths of UK-based Toople's (TOOP) value was wiped off following fundraising of £1.41m for marketing and customer acquisition activities. The company has struggled on the stock market, its share price declining by approximately 75% since its IPO last year.
Investors lost their appetite for Lebanese canteen group Comptoir (COM) as it struggled with an unexpected decline in like-for-like sales and profit in May. The restaurant business continued to underperform on the stock market after scaling back expansion plans in April. Shares in the company crashed 28% to 22.6p.
Three new contract wins at Cape (CIU) failed to distract investors from the bumpy outlook for the company as its shares slumped 3.8% to 232.7p. The board warned that 2018 will be a more challenging year, driven by an expected reduction in volumes in Asia Pacific and project delays in the Middle East.
In the recruitment sector, Dillistone (DSG) warned its full year results were likely to be significantly below market forecasts as it suffered a slow start to 2017 and a higher cost base. The stock plummeted 14.8% to 72p.
Elsewhere, shares in Genel Energy (GENL) slumped 11.6% to 87.2p after co-founder Nat Rothschild's decision to step down from his role of non-executive director.
Qatar Investment Fund (QIF) declined 6.9% after several of Qatar's neighbours severed diplomatic ties with the Arab state over its alleged backing for Islamic militants.