SUCRE - Bolivian opposition senator Jeanine Áñez has declared herself interim president of the South American country following Evo Morales' resignation.

Ms Áñez said she was next in line under the constitution and vowed to hold elections soon.

Her appointment was endorsed by Bolivia's Constitutional Court.

Lawmakers from Mr Morales' party boycotted the session, and the former president branded Ms Áñez "a coup-mongering right-wing senator".

Mr Morales has fled to Mexico, saying he asked for asylum there because his life was in danger.

He resigned on Sunday after weeks of protests over a disputed presidential election result. He has said he had been forced to stand down but had done so willingly "so there would be no more bloodshed".

Ms Áñez, 52, is a qualified lawyer and a fierce critic of Mr Morales. She was previously director of the Totalvision TV station, and has been a senator since 2010, representing the region of Beni in the National Assembly.

As the deputy Senate leader, Ms Áñez took temporary control of the body on Tuesday after Bolivia's vice-president and the leaders of the senate and lower house resigned.

That put her next in line for the presidency under the constitution.

The parliamentary session to appoint Ms Áñez was boycotted by lawmakers from Mr Morales' leftist Movement for Socialism party, who said it was illegitimate.

"Before the definitive absence of the president and vice president... as the president of the Chamber of Senators, I immediately assume the presidency as foreseen in the constitutional order," Ms Áñez said to applause from opposition lawmakers.

Bolivia's highest constitutional court backed her assumption of power.(FA)