Venezuela's vice president has been sworn in as interim president, just hours after hundreds of thousands of mourners attended the state funeral of late President Hugo Chavez.
Nicolas Maduro’s swearing-in on Friday took place at the National Assembly in the capital Caracas.
It had earlier been set to be staged in the same military academy where the funeral - attended by more than 30 heads of state - was held.
"I swear by the most absolute loyalty to comrade Hugo Chavez that we will fulfill and see that it's fulfilled the constitution ... with the iron fist of a people ready to be free," Maduro, 50, said at his swearing-in.
Venezuela's opposition coalition had announced through spokesman Angel Medina that it would boycott the inauguration of Chavez's hand-picked successor, calling it "fraudulent".
Henrique Capriles, tipped as the opposition's candidate in upcoming elections, said: "Nicolas, nobody elected you president. The people didn't vote for you, kid".
Capriles, who lost to Chavez in the October presidential election, argued that the constitution requires the vice president to step down from his post in order to run for president.
He also said Maduro had used the funeral earlier in the day to campaign for the presidency.
The country's Supreme Court has ruled that Maduro could become acting president while polls were called within 30 days.
Call for election
Shortly after his swearing-in, Maduro urged the national electoral council to "immediately" call an election.
He said he had officially asked Tibisay Lucena, the council president, to "immediately convene presidential elections".
Maduro also named Jorge Arreaza, Chavez's son-in-law and Venezuela's science and technology minister, as his vice president.
Arreaza had frequently been at the side of the dying president in his final weeks, sometimes providing updates about his health.
Both Maduro and Diosdado Cabello, the National Assembly president, pledged to follow Chavez's example and push his socialist-inspired agenda.
In a post-inauguration speech, Maduro echoed accusations he made shortly before Chavez's death that the US had caused the fatal cancer.
He referred to "this illness very strange for the speed of its growth and for other scientific reasons that will be known in their moment".
He later touched on Chavez's penchant for criticising "the empire", his term for the US.
"We tell them: Sooner than later, the imperialist elites who govern the United States will have to learn to live with absolute respect with the insurrectional people of the ... Latin and Caribbean America," Maduro said.
Earlier on Friday, Maduro featured prominently at Chavez's funeral, receiving a ceremonial sword, which is a replica of the sword carried by Simon Bolivar, the Latin American liberator.
Maduro is a former bus driver who quickly became a union leader. He had been foreign minister since 2006. Chavez then tapped him as his vice president three days after winning re-election last year.
Chavez, 58, died on Tuesday after a two-year battle with cancer, ending his 14-year rule over the country.
Underscoring Chavez's talent for uniting a mix of perhaps unlikely allies, the centre-right presidents of Chile and Colombia attended his funeral, as well as Western idealists like actor Sean Penn and US civil rights leader Reverend Jesse Jackson.
Jackson recited a prayer, urging God to "heal the breach between the US and Venezuela."
Later, speaking to Al Jazeera, Jackson said he did not endorse any Venezuelan presidential candidate, but supported an "orderly transition".
Presidents Mahmoud Ahmadinejad of Iran and Alexander Lukashenko of Belarus sat next to each other, wiping away tears as a band played one of Chavez's favourite sentimental songs.
"We have lost a great leader, a great man," Ahmadinejad said after the ceremony.
"Hugo came from the people and he served the people."
Several Latin American leaders, including Cuban President Raul Castro, were invited to stand around the coffin.
European nations sent lower-level delegations while the US was represented by its charge d'affaires and two Democratic Party politicians.
Chavez's body will lie in state for seven more days and officials said his body will be embalmed and preserved "like Lenin" to rest in a glass casket in the military barracks.