Crude oil futures dropped on Thursday by more than 1 per cent, ending May with their biggest monthly decline in more than three years as bloated US stockpiles and weak economic data added to worries about the euro zone crisis, all dampening oil demand prospects.

Oil pared sharp losses of more than 2 percent in afternoon trading, after Dow Jones reported that the International Monetary Fund was considering a rescue loan to beleaguered Spain if it failed to bail out a big bank.

But IMF Managing Direcrtor Christine Lagarde later denied the report.

'There is no such plan. We have not received any request to that effect and we are not doing any work in relation to any financial support,' Lagarde said in a statement.

Fears about potential oil supply disruption and a new Mideast conflict as Iran resumed talks with world powers over its disputed nuclear program had kept oil futures range-bound in recent weeks. But with growing signs of weakening growth in China, Europe and to some extent, the United States, investors have become leery of adding bullish bets on crude futures.

'The latest series of US data has snuffed out recent silver linings that had kept growth moving, though at a slow pace, and Europe is imploding,' said Mark Anderle, trader at TAC Energy in Dallas.

'Technical support has also vanished, so now you have a perfect cocktail for selling,' he added.

Crude futures slumped to seven-month intraday lows after official data showed that US crude oil stockpiles swelled last week, hitting the highest level in nearly 22 years.

Oil prices trudged downwards earlier on disappointing US economic reports that worsened the outlook for global oil demand prospects, already dampened by the worsening euro zone crisis, and slower growth in China and India.

US crude oil inventories, excluding strategic reserves, rose much more than expected last week to hit their highest level since July 1990, US Energy Information Administration (EIA) date showed. That quickened the day's selling.

The euro sank in volatile trading against the dollar, touching a 23-year low against the greenback on concerns about Spain's banking troubles and weak US economic data. In turn, investors pared their holdings in riskier  commodities and equities assets.

In London, ICE Brent crude futures for July delivery  settled at $101.87, down $1.60, the lowest finish for front-month Brent since Oct. 4.

Front-month Brent fell 14.7 percent for the month, its biggest monthly decline since December 2008, after slipping 3 percent on Wednesday. Brent has fallen more than 21 percent from its 2012 high of $128.40 hit in March.

US crude for July delivery settled at $86.53, falling $1.29, and marking the lowest US front-month close since Oct. 20.

Front-month US crude sustained a 17.5 percent loss for May, its biggest monthly decline since December 2008. It has dropped more than 22 percent from its 2012 peak of $110.55 struck in March.

Brent's premium against US crude rose as high as $15.99, but narrowed at the close to $15.34 as US government data showed that crude oil stockpiles at the US delivery point in Cushing Oklahoma, while reaching a new record, edged up only modestly from the previous week's levels.

Traders expect that the reversal earlier this month of the Seaway pipeline from the US delivery point in Cushing, Oklahoma, to the main US refining center in Gulf Coast, will help ease the glut of oil in the US Midwest and possibly move US and Brent crude prices closer.

Brent's volume topped more than nearly 670,000 contracts,  23 percent above its 30-day average, ahead of the US trading volume of almost 612,000 contracts, 18 percent atop its  30-day average, according to Reuters data.

Euro zone crisis

The crisis in the euro zone continued to dominate market sentiment.

'Markets have been fairly tight but it's all these euro zone worries that have really spooked the oil markets,' said Rob Montefusco, a trader at Sucden Financial.

Mario Draghi, president of the European Central Bank, warned that the ECB could not fill the vacuum created by the lack of action by national governments.

Spain's center-right government has so far failed to spell out how it plans to finance a 23.5 billion euro ($29 billion) rescue of Bankia, the country's fourth largest lender.

Gasoline falls, jobs data awaited

US gasoline futures closed the month at a four-month low,  pressured by continuing weak demand, despite falling stockpiles.

US gasoline for June delivery expired and settled at $2.8250 a gallon, down 3.32 cents, the lowest close for front-month gasoline since Jan. 24. Prices fell as investors ignored data showing US gasoline inventories fell last week to the lowest level since 2008.

On Friday, traders shift their sights to the all-important US nonfarm payrolls and unemployment data for May to see if the economy's modest recovery is still holding.

US employers were expected to have hired 150,000 new workers during the month, after a disappointing rise of just 115,000 in April, according to a Reuters poll. The unemployment rate probably remained unchanged at the 8.1 percent level, the poll also showed. – Reuters