US crude oil prices dropped to nearly $40 a barrel on Thursday, following an increase in supplies in North America and the Middle East due to surge in imports, as well as rise in stockpile.

Brent crude futures fell 75 cents to $46.41 a barrel, while US crude oil, also known as West Texas Intermediate, or WTI, slipped 50 cents to $40.30 a barrel, Reuters reported.

PVM Oil Associates director and technical analyst Robin Bieber said in a note to clients of the London brokerage: "The trend is down and vicious."

"Concerns over the pace of economic growth in emerging markets contributed to the changed forecast."

According to the Energy Information Administration (EIA), last week US crude stockpiles increased by 2.6 million barrels to 456.21 million barrels.

There was a slight increase in inventories as a US refinery closed for repairs last week.

Since June, US crude oil production decreased by over 250,000 barrels per day (bpd).

Energy Information Administration has also lowered the crude oil price forecasts, saying that West Texas Intermediate (WTI) crude oil prices would hover around $49 per barrel during 2015, and $54 a barrel in 2016.

EIA said in its latest forecast: "Concerns over the pace of economic growth in emerging markets, continuing (albeit slowing) supply growth, increases in global liquids inventories, and the possibility of increasing volumes of Iranian crude oil entering the market contributed to the changed forecast."

It also added that North Sea Brent has been trading $5 per barrel more than WTI since the beginning of this year, and it will continue through 2016.

OPEC continues to pump record levels of oil, adding to the global supply glut, with Saudi Arabia exporting 7.365 million bpd in June, according to industry data.