Echeverria was interior minister at the time of the killings

The ailing Mr Echeverria, under house arrest since Friday, made the declaration before a judge at his home.

He is accused of involvement in the deaths of up to 300 students when troops opened fire on protesters.

"Nothing proves that I was the author of or participated in any crime," Mr Echeverria said in a written statement.

'Absurd distortion'

Mr Echeverria's legal team said that although 43 protesters and troops were killed in clashes during the protest, this was not because of any "state policy of extermination".

Mexican students still mark the 1968 Tlatelolco massacre

"To say that genocide was committed against students on 2 October 1968 is an absurd distortion of the clash that happened that day," his statement said.

Mr Echeverria was interior minister in 1968 at the time of the killings in Tlatelolco Square.

Prosecutors say up to 300 people may have died when government agents hidden among regular soldiers opened fire during the protest, which took place days before the Olympic Games opened in Mexico City.

But the former president denies allegations that he posted snipers on scores of buildings and gave orders to shoot.

'Dirty War'

In a surprise ruling last week, an appeals court ruled that there was enough evidence to support a charge of genocide against Mr Echeverria and ordered his arrest.

Outside the former president's residence, survivors of the clashes displayed signs reading "prison for the assassin" and called for his hearing to take place in public.

His lawyer, Juan Velasquez, has told the Associated Press news agency that Mr Echeverria would not serve time in prison because of his age.

Special prosecutor Ignacio Carillo has tried and failed twice previously to bring genocide charges against Mr Echeverria.

Hundreds died or disappeared during Mexico's "Dirty War" on leftists under Mr Echeverria's presidency between 1970 and 1976.

Outgoing Mexican President Vicente Fox, who leaves office in December, has vowed to bring to justice those responsible for killings and oppression in the country's past.