Venezuela's President Hugo Chavez, 58, died on Tuesday after a long battle with cancer.
Chavez, who stayed in power14 years, had undergone several operations in Cuba, and had not been seen in public for several months.
Foreign Minister Elias Jose Jaua Milano declared seven days of mourning and said Mr Chavez's body would lie in state until his funeral on Friday.
Vice-President Nicolas Maduro would assume the presidency until an election was called within 30 days, he added.
"It is the mandate that Comandante President Hugo Chavez gave us," Mr Jaua told state television, adding that Mr Maduro would also be the candidate of the governing United Socialist Party (PSUV).
It was not immediately clear when the election would take place.
Mr Chavez's illness prevented him from taking the oath of office after he was re-elected for a third term in October and the President of the National Assembly, Diosdado Cabello, had been expected by some to take over as interim president in the event of his death.
However, he was not among the political and military leaders who flanked the vice-president when he announced Mr Chavez's death.
In Tuesday's televised address, Mr Maduro said the president had passed away "after battling a tough illness for nearly two years".