The Indian rupee today strengthened by 15 paise to 45.91 rupees per US dollar in early trade on the Interbank Foreign Exchange as the dollar weakened against the euro and other currencies and a rally in the domestic stock market. Forex dealers said dollar weakness against the euro and some Asian currencies overseas and a higher opening in the domestic stock market helped the rupee to strengthen. On Monday, the rupee had ended 9 paise higher at 46.07 rupees against the US dollar, helped by strong rebound in stock markets.