At the interbank foreign exchange market, the rupee strengthened 79 paise its biggest single day gain so far this year to close at a one-month high of 65.67 against the dollar.At the stock markets, the Sensex at the Bombay Stock Exchange gave up much of its initial gains, but still ended 255 points higher, at 26,219. During the session, the Sensex had surged as over 500 points. The Nifty at the National Stock Exchange jumped 83 points, to 7,982. Other key Asian markets in China, Japan, South Korea, Hong Kong and Singapore ended mixed. But major European bourses in the UK, Germany and France lost considerable ground.