Congress seemed likely to have more than 200 seats in the Lok Sabha or parliament once all the votes are counted, The Hindu reported. With its allies in the United Progressive Alliance, the party would have more than half of the 543 parliamentary seats.
The victory makes Manmohan Singh the first prime minister since Jawaharlal Nehru to lead his party to victory after a five-year term, the newspaper said. Congress President Sonia Gandhi, appearing at a news conference with Singh, made it clear that he would remain in office.
"The people of India have spoken, and spoken with great clarity," Singh said, appearing at a news conference with Gandhi.
Gandhi, widow of Nehru's grandson, said that Singh would decide whether to name her son, Rahul Gandhi, to the Cabinet.
Before the vote counting began, there were predictions of a close race between Congress and the Hindu nationalist BJP party. The outcome denied any chance to help form a government to the Third Front, a left-wing alliance including the Communists and some regional parties with Congress.
The Congress Party's allies, Trinamool Congress and Dravida Munnetra Kazhagam, also were successful in the national elections, PTI said.
UPA's rival, the National Democratic Alliance, had garnered 166 seats to date, thanks mainly to the Bharatiya Janata Party taking 50 seats and leading in 67 more.
BJP leader Arun Jaitley has admitted defeat in the Indian elections, following Third Front leaders in accepting the victory by the Congress Party and its alliance, the BBC reported.
"We accept this verdict," Jaitley said. "Something certainly did go wrong. ... Our performance was not up to expectation."
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