U.S. oil prices fell over 3 percent on Monday on concerns a six-week market recovery has gone beyond fundamentals, as U.S. crude stockpiles continue to mount and Iran maintains little interest in a global production freeze.

Market intelligence firm Genscape reported an inventory build of 585,854 barrels in Cushing, Oklahoma, taking the delivery hub for U.S. crude futures closer to capacity, traders who saw the data said.

The Organization of the Petroleum Exporting Countries said global demand for crude from its members, including Saudi Arabia, Iraq and Iran, will be less than previously thought in 2016 due to competing non-OPEC supply. OPEC supply will likely exceed demand by about 760,000 barrels per day, up from 720,000 bpd implied earlier, it said.

Russia said OPEC's meeting on a production freeze with other key oil producers like itself will probably be held in Doha in next month. It said Iran supports the plan, although Tehran was keen to restore its crude exports first to pre-sanction levels.