The rupee today slumped by 20 paise against the US currency after a sharp fall in stock markets following concerns over the Greece's debt crisis.

Month-end dollar demand from importers, mainly oil refiners, too weighed on the rupee, dealers said.

After fairly active trade at the Interbank Foreign Exchange (Forex) market, the domestic currency closed at 44.64/65, down 20 paise over the previous close.

The US dollar accelerated gains in late yesterday's trading session, pushing the Euro to a one-year low, after Standard & Poor's lowered Greece's ratings for below investment grade and cut Portugal's long-term ratings by two notches.

The dollar today touched 11-month high in London against its major rivals after worries over debt problems in Greece propelled safe-haven demand for the US currency.

The benchmark Sensex today plunged by a whopping 310.54 points or 1.76 per cent, highest fall since February 5, putting pressure on the rupee, dealers said.

Meanwhile, global crude oil prices were trading above USD 82 a barrel in London today.

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