Oil prices fell today after the US central bank warned on the health of the global economy and bearish signs persisted that the world's biggest crude producers would keep pumping at high levels.

The Federal Reserve decided against raising interest rates from historic lows on Thursday, saying uncertainty about global economic growth had forced its hand.

The bearish sentiment sent European and US stock markets sharply lower, with Frankfurt's DAX down more than 3% and the US S&P 500 index down 1.15% shortly before 3pm.

The oil market had mixed reactions to the Fed decision, with concerns about economic weakness sending commodities lower, but a fall in the US currency also meant buying dollar-traded crude became cheaper.

"The perception of 'ZIRP (Zero Interest Rate Policy) forever' should provide some underlying support to the commodity complex," said Olivier Jakob, a strategist at Petromatrix, a Swiss-based consultancy.

Brent crude was down 80 cents at $48.28 a barrel at 2.40pm, after touching an intraday high of $49.75.

US West Texas Intermediate (WTI) crude futures were trading down $1.55, or 3.3%, at $45.35 a barrel.

Brent was set to make its first weekly gain in three weeks, hinting at a turn in momentum for a commodity that has declined nearly 30% since spring.

Kuwait, a member of the Organisation of the Petroleum Exporting Countries (OPEC), said on Thursday the oil market would balance itself but that this would take time, indicating support for the group's policy of defending market share despite falling prices.

Other sources at OPEC backed this view, saying they expected oil prices to rise by no more than $5 a barrel per year to reach $80 by 2020, with a slowing in rival non-OPEC production growth not enough to absorb the current oil glut.

Iran's deputy oil minister Rokneddin Javadi was quoted as saying the country would unveil new oil contracts in the coming weeks, earlier than previously expected.

The prospect of sanctions-free Iran adding more barrels to an already oversupplied market is fuelling bearish momentum.

Mr Javadi also reiterated Iran's plans to regain its oil production share once Western sanctions are removed.

Russia acknowledged for the first time today it would cut production if oil prices fall below $40 a barrel, floating the possibility that one of the biggest oil producers may resort to proactive measures to prop up prices.