Crude oil prices on Monday continued a steep decline sparked by the British vote to leave the European Union, with London warning of continued volatility ahead.

"There is the volatility we have seen and are likely to continue to see in financial markets," British Chancellor of the Exchequer George Osborn said in a statement Monday.

Major world stock indices collapsed Friday after a narrow vote in favor of the British referendum to leave the EU, with U.S. markets losing an entire year's worth of gains. By his own account, Osborn said the markets were not expecting the referendum result that emerged last week.

"It will not be plain sailing in the days ahead," he warned.

The price for Brent crude oil, the global benchmark based on oil found in the North Sea, lost 1.7 percent to start the day in New York at $47.60 per barrel. West Texas Intermediate, the U.S. benchmark for oil, was off 1.6 percent to open at $46.88 per barrel.

Since the start of trading Thursday, the day of the referendum, Brent is down more than 6 percent.

Last week's collapse was punctuated by data from oilfield services company Baker Hughes, which reported a decline in North American rig activity, a reversal from previous week's trends that mirrored oil's slow march back toward the $50 per barrel mark.

U.S. Secretary of State John Kerry meets Monday with British and European leaders to discuss the fallout from the so-called Brexit. Speaking from Italy during the weekend, Kerry said the EU without the United Kingdom was still "a very powerful" economy.

"The most important thing is that all of us as leaders work together to provide as much continuity, as much stability, as much certainty as possible in order for the marketplace to understand that there are ways to minimize disruption," he said in a statement.

Last week, Moody's Investors Service downgraded the long-term British debt rating from stable to negative. The referendum, it said, should usher in a long period of uncertainty that will have negative effects on the country's mid-term economic growth prospects. It may take "several years" for British policymakers to reconfigure its economic relationship with the rest of the world.

By the start of trading Monday in New York, the FTSE 100 Index in London was down about 1.8 percent.