Global oil inventories could rise sharply despite an agreement by OPEC and its allies to deepen output cuts as well as lower expected production by the U.S. and other non-OPEC countries, the International Energy Agency (IEA) said on Thursday.

"Despite the additional curbs ... and a reduction in our forecast of 2020 non-OPEC supply growth to 2.1 million barrels per day (bpd), global oil inventories could build by 700,000 bpd in Q1 2020," the IEA said in a monthly report.

The OPEC and other producers agreed last week to rein in output by an extra 500,000 bpd in the first quarter of 2020 in order to balance the market and buoy prices.

Even if the group adhered strictly to the new pact and output from members beset by political troubles like Iran, Libya and Venezuela stayed steady, the IEA said only 530,000 bpd of crude would be withdrawn from the market compared to November production.

The IEA revised down its forecast for supply growth by non-OPEC countries in 2020 by 200,000 bpd "on a continued slowdown in the U.S., reduced expectations for Brazil and Ghana as well as additional cuts by (OPEC's allies)".