86-year-old denies he was complicit in rape, torture and murder of indigenous civilians by troops during his rule in 1980s

The former Guatemalan dictator Efraín Ríos Montt has made a last-gasp effort to assert his innocence as judges prepared to rule on the charges of genocide and crimes against humanity that he faces.

Breaking the silence he has maintained until now in the historic case, the 86-year-old used his closing statement on Thursday to deny claims that he was responsible for the deaths of at least 1,771 Mayan Ixils.

Prosecutors have alleged that, as head of state and the military for 17 months from 1982, Ríos Montt was complicit in the rape, torture and murder of indigenous civilians carried out by his troops during a counter-insurgency campaign in the heartlands of the leftist guerrilla movement.

In an hour-long rebuttal, the elderly defendant blamed his field commanders, who he said acted autonomously.

"I never authorised, I never signed, I never proposed, I never ordered an attack against any race, against any ethnic group," he told the court. "I never did it, and of everything that has been said here, there has never been any evidence of my participation."

Ríos Montt's intervention provided a dramatic finale to a fraught, month-long court case that has rekindled painful memories of one of Latin America's bloodiest civil wars.

An estimated 200,000 people died during the 36-year conflict, while 45,000 others "disappeared". The targeting of the Mayan population – in an attempt to undermine support for the insurgents – was one of the grimmest episodes of the battle for control of the country that finally ended in 1996 with a peace accord.

The prosecutor Orlando López wrapped up the case against Ríos Montt by summarising the testimonies of almost 100 witnesses: 94 had lost a family member, 83 had suffered arson attacks, 16 were sexually assaulted and seven were tortured. He said forensic experts had examined mass graves that showed many victims, including children, were killed in assassination-style shootings.

Having presented detailed plans of the chain of command and testimony from former officers, López said Ríos Montt must have had full knowledge of the army operations. He demanded 75 years in prison for the former dictator and his co-defendant, the former intelligence chief José Mauricio Rodríguez Sánchez.

Both defendants deny the charges.

Ríos Montt, who took and lost power as a result of coups, said the Guatemala he inherited was a failing, bankrupt nation that was full of "subversive guerrillas". But he insisted that he never ordered genocide.

Since hearings opened last month, the case has become increasingly heated. Earlier this week, the defence lawyer García Gudiel reportedly challenged the authority of the three civilian judges and warned them: "I will not rest until I see you behind bars."

A verdict and sentence are expected shortly.