Dr Singh, United Progressive Alliance chairperson Sonia Gandhi, a number of cabinet ministers and senior Congress leaders, including Delhi Chief Minister Sheila Dikshit, visited Mrs Gandhi's memorial Shakti Sthal in Delhi and paid floral tributes at her samadhi.
Later, an all-religion prayer was held at the All India Congress Committee headquarters, attended by the prime minister, the Congress president and other party leaders, including Mr Rahul Gandhi.