Conservative senator Jeanine Anez was unknown to many Bolivians before she stepped out beaming and waving a Bible on the balcony of the government palace.
A longtime critic of her leftist predecessor Evo Morales, she stepped into the power vacuum left when he suddenly fled the country to escape a violent crisis.
Now all eyes in the country are on Ms. Anez, a 52-year-old lawyer from the northeastern region of Beni, bordering Brazil.
As second deputy speaker of the Senate, Ms. Anez was sworn in by her allies after all the other officials in line to act as interim president had fled.
Fresh from being sworn in, she posed with a purple Bible in her hand and the green, yellow and red presidential sash across her shoulder, waving to supporters with a broad smile.
A proud Christian, she immediately made a point of marking herself out from Mr. Morales, a socialist who had done away with religious oaths of office.
At one point she raised above her head a big old leather-bound copy of the Gospels.
“God has allowed the Bible to come back into the (presidential) palace. May he bless us,” she said.
She cast herself as the only one in a position to lead the country out of its crisis, sparked by claims that Mr. Morales rigged his re-election last month.
“According to constitutional order, it is my role to take up this challenge with the sole aim of calling new elections,” she said in televised comments.
“I am committed to take all measures necessary to pacify the country,” she said later at her swearing-in session.
Mr. Morales branded her “a coup-mongering right-wing senator.”
He said she had “declared herself... interim president without a legislative quorum, surrounded by a group of accomplices.”
Minority party
Ms. Anez became the South American country’s 66th president and the second woman to hold the post.
The last woman to serve as Bolivia’s president was Lidia Gueiler, who held the post for less than two years before being deposed in a military coup in 1980.
Ms. Anez promised to hold fresh elections “as soon as possible”.
“It’s a commitment we have made to the country and of course, we will fulfil it.”
By doing so she aims to settle a deadly crisis that erupted after Mr. Morales ran for a fourth term as President.
A trained lawyer, Ms. Anez served from 2006 to 2008 as member of an Assembly that drew up the current constitution. She has been a senator since 2010.
She is a member of a minority conservative political group, Democratic Unity.
She was named second Deputy leader of the Senate in line with a tradition that all parties be represented in the top posts.
Stepping in
Mr. Morales fled to Mexico on Sunday after three weeks of violent unrest following the election.
Several of his allies who held senior posts also fled, leaving Ms. Anez the most senior official still standing.
She declared that it was up to her to take the reins of power “immediately.”
Her swearing-in, approved by the Constitutional Court, sparked jubilation in her hometown of Trinidad.
Opponents of Mr. Morales also celebrated in La Paz and other major cities.
Ms. Anez has supported the use of the “wiphala” flag alongside the Bolivian national flag.
The wiphala is a multicolored symbol of Andean indigenous peoples that is waved by supporters of Mr. Morales, the country’s first indigenous president.
Referring to the accusations against Mr. Morales, Ms. Anez vowed that “never again” would an election be rigged.
She called a minute of silence for seven people who been killed in the recent weeks of unrest.
Bolivian media reported that Ms. Anez is divorced and has two children aged 29 and 24.
