People work at the Halfaya oilfield in Amara, southeast of Baghdad.

hit a more than three-year high on Thursday, breaking through the psychologically important $70 a barrel level for the first time since December 2014.

Oil futures failed to hold the gains, selling off as the close of trading approached, with analysts warning that the market might have little room left to run.

Brent, the international benchmark for oil prices, was last up 6 cents at $69.26 a barrel. It earlier spiked to $70.05 in morning trade, touching its highest level since Dec. 4, 2014, when the contract hit $70.60.

U.S. West Texas Intermediate crude finished the session up 23 cents at $63.80, after breaking through $64 a barrel for the first time since December 2014. The contract topped out at $64.77, a high going back to Dec. 8, 2014.

Oil prices have been supported by stronger-than-expected demand fueled by worldwide economic growth, ongoing output limits by OPEC and Russia and a series of global events that have stoked geopolitical tension.

A rally that began in June accelerated in December, with prices rising about 15 percent over roughly the last month.

"I think it starts to get difficult for us to get much higher from here," said John Kilduff, founding partner at energy hedge fund Again Capital. "I think we're probably in the process of topping out as we speak."

Kilduff forecast last week that Brent would take aim at $70 a barrel and U.S. crude could break into the $65-$67 range. But high prices will tempt OPEC members and other producers to start pumping, he said.

About two dozen oil producing nations are keeping 1.8 million barrels a day off the market to drive down global inventories to their five-year average.