Guatemala's highest court on Tuesday ordered that the genocide trial against one of the Central American country's former dictators be taken over by a judge who wants the proceedings to go back to Square 1.

A spokesman for the Constitutional Court, Martin Guzman, said the case of Efrain Rios Montt now goes back to Judge Carol Patricia Flores, who last week ordered that the proceedings start over at a point before the retired general was charged with genocide.

Rios Montt, 86, is accused of responsibility for the deaths of 1,771 Mayan Indians killed during military offensives by the dictatorship that he headed from March 1982 to August 1983. The operations, during a U.S.-backed war against leftist guerrillas, were part of a "scorched earth" campaign aimed at wiping out support for the rebels.

The trial against Rios Montt and Jose Rodriguez Sanchez, 68, a former high-ranking member of the military chiefs of staff, had been nearing closing arguments last week when Flores intervened.

Flores had handled the case in its pre-trial stage, but was taken off the case in February 2012 by an appeals court after the defence filed a complaint saying she was biased against the defendants. She was reinstated last week by the Constitutional Court, then ruled that all actions taken in the case since she was first asked to step down in November 2011 were null.

Neither Rios Montt's lawyers nor attorneys for the plaintiffs returned calls from The Associated Press seeking comment on Tuesday's action.

Many speculated that Flores's ruling was politically motivated in the much-disputed trial, which is the first genocide case against a former president in Latin America. In weeks of testimony from dozens of victims, soldiers and experts, even current President Otto Perez Molina had been implicated in the massacres.

UN advisor warns against political interference

The move caused an international outcry. Before the high court's decision was announced Tuesday, the United Nations special advisor on the prevention of genocide, Adama Dieng, urged Guatemalan authorities to bring justice for the victims and their families.

"I appeal to judicial authorities to act responsibly and to prevent any interference, obstruction or manipulation of justice, which would seriously undermine the credibility of the justice system in Guatemala," Dieng said in a statement.

[IMAGEGALLERY galleryid=3959 size=small]

"The victims of the atrocities committed during the civil war in Guatemala, as well as their families, have been waiting many years for justice. I hope they don't have to keep waiting. Justice delayed is justice denied."

About 500 Ixil Mayan Indians arrived in the capital to show their support in favour of Rios Montt in buses with banners that read "Do not shame the Ixil with that idea of genocide, because that's a lie."

The demonstrators arrived from Nebaj in the state of Quiche, an area where some of the worst massacres were carried out by the army.

The trial against Rios Montt started in March after courts dealt with more than 100 complaints and injunctions filed by the defence. Since then, the court has heard the harrowing testimony of dozens of people who survived the military offensive.