UN Secretary-General Antonio Guterres on Sunday voiced his deep concern about the situation in Bolivia following weeks of unrest that culminated in the resignation of President Evo Morales.

Morales, whose re-election victory triggered weeks of protests amid fraud allegations, announced his resignation on Sunday after the military demanded his departure.

The UN chief urged all concerned in Bolivia to refrain from violence, reduce tension and exercise maximum restraint, said Stephane Dujarric, Guterres' spokesman, in a statement.

Guterres called on all actors to abide by international law, notably fundamental human rights principles, said the statement.

The secretary-general also appealed to all actors to commit to achieving a peaceful resolution of the current crisis and to ensuring a transparent and credible re-run of the elections, it said.

Some analysts have called the Bolivian crisis a "coup", as the resignation tendered by Morales was pressured by a powerful military that has often acted in tandem with American foreign policy ambitions. Morales, who was a socialist leader from Bolivia's indigenous community, was thought to not have American favor.

If the American government is discovered to be involved in the crisis, it will be another coup in a history of US-backed coups in South America against leaders that are perceived as "anti-American".

Fearing execution by the military, the Bolivian leader Morales has fled to Mexico.