The United Progressive Alliance (UPA) of which the Congress (I) party is the principal constituent, won a clear victory in the parliamentary election and has raised hopes of greater economic reforms.
Dr Singh is the first prime minister since the country´s post-independence leader Jawaharlal Nehru to be returned to office after completing a full term.
The Congress said it had the support of 274 lawmakers before the DMK exit, two more than needed for a parliamentary majority. DMK said it would support the UPA government from outside following a row over ministerial positions.
"We have support of 322 parliamentarians and we are not worried about falling short at all," Janardhan Dwivedi, a senior Congress leader, said.
Earlier, the Prime Minister´s Office said in a release that today´s exercise will be followed in the next few days by an expansion of Council of Ministers including other cabinet ministers, ministers of state with independent charge as well as other ministers of state which will give due representation to allied parties.
Veteran Congress leader and former cabinet minister for Human Resources Development, Arjun Singh, has been dropped.
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