Image copyright AP Image caption Janet Yellen said the Fed was unlikely to raise rates for "at least a couple of meetings"

The US Federal Reserve has altered its tone on potential interest rate moves.

Its statement, issued on Wednesday after the conclusion of a two-day meeting, said it would be "patient" in deciding when to raise interest rates.

Previously the US central bank said it would keep interest rates low for a "considerable time".

Central banks of necessity speak in highly guarded language, but most analysts interpret this as meaning a rate rise could come in mid-2015.

The US economy has been growing strongly with unemployment falling, conditions that would normally lead to higher inflation and an increase in the cost of borrowing.

However, shrinking economic growth rates in developing countries, most importantly in China, and political instability in Russia and the Middle East have undermined confidence that this growth can persist.

On top of that, oil prices have halved since the summer, bringing down the cost of transport and a wide range of goods.

The Federal Reserve chairman, Janet Yellen, explained that "patient" meant the bank was unlikely to raise rates for "at least a couple of meetings".

That would mean April next year at the earliest.