Oil prices fell today after a rise in weekly US crude inventories fed into bearish sentiment about the deepening global supply glut that has brought oil prices close to 12-year lows.

Brent crude, the global benchmark, was down 37 cents at $30.49 a barrel late in the afternoon.

US West Texas Intermediate crude (WTI) was down 30 cents at $30.13 a barrel. Both contracts saw intra-day highs of more than $1 above Tuesday's closing price on upbeat Chinese economic data earlier in the session.

"Overall, it's a bearish report. I think today's inventory report is all about products... The long awaited massive decline in crude production is not starting again," said Dominic Chirichella, senior partner at Energy Management Institute in New York.

US crude inventories rose by 234,000 barrels in the last week, compared with analysts' expectations for an increase of 2.5 million barrels, according to the government's Energy Information Administration.

Analysts at Morgan Stanley warned on Wednesday that a rise in demand for crude could be lower than previously expected.

"Any slowing in the rate of demand growth could delay the timing of rebalancing and ultimately a price recovery," they said in a research note.

The potential for the calling of an emergency OPEC meeting also weakened on Wednesday when Iran's oil minister was quoted as saying he had not received any request for such a gathering.

Nigeria's oil minister said on Tuesday that a "couple" of OPEC members had asked for an emergency meeting.

Days ahead of the expected implementation of a landmark nuclear accord between Tehran and world powers, Iran briefly detained a group of US sailors after they entered Iranian waters.

Iran released the sailors today after holding them overnight, determining they had entered Iranian waters by mistake.