In a statement on Tuesday, Menachem Mazuz, the attorney general, announced that he planned to indict Katsav on suspicion that he raped a former staff member and sexually assaulted three other women who worked for him.
Katsav called the allegations "smears and lies" that were "terrible, hurtful" and said: "I will fight to my last breath to clear my name."
He said he had already suffered a "trial by media".
Appeal to the citizens
Analysts saw Katsav's speech as an attack on the media and an appeal to public opinion.
He appealed directly to the citizens of Israel, saying: "As time goes by and as the facts emerge you, the citizens of Israel, will understand what terrible injustice has been done here."
Gill Hoffman, a journalist with the Jerusalem Post, told Al Jazeera: "He [Katsav] was really talking to the media and the Israeli citizens rather than members of the knesset [Israeli parliament]. A lot of Israelis will sympathise with him - they will now question what they thought before."
"I have no doubt that the president cannot continue and fulfil his position and he should leave the residence of the president of Israel"
Israeli prime minister
Jacky Rowland, Al Jazeera's correspondent in Israel, said: "He was trying to appeal over the heads of the opinion makers.
"The bottom line is that the fact that any allegations have been made against him casts a stain over the presidency.
"And people feel the president, in the interests of the dignity of the office that he holds, should step down."
Earlier in the day Katsav notified the Knesset that he was taking a leave of absence from his duties.
Dalia Itzik, the Knesset speaker, will temporarily fill the position - the first time the country has had a female president.
Under Israeli law, the president cannot be put on trial while in office but the Knesset does have the power to impeach him.
But analysts say an investigation could take over a year and Katsav's presidency is due to end in July.
Mazuz said he would invite Katsav and his lawyers to a hearing, the date of which has not been set, before finalising charges.
Katsav has said he will resign if he is charged.
" I don't really care whether Olmert stays or someone else comes, unless they are sincere enough to do something about the current conflict"
Far, Lahore, Pakistan
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Nour Odeh, Al Jazeera's correspondent in Gaza, said that Palestinians, who are also experiencing internal political conflict, "know that when there is internal trouble in Israel, it is Palestinians who end up paying the price".
She also said the events were "a further indication to Palestinians not to put their faith in Israeli politicians".
The post of president in Israel is largely ceremonial and the case is unlikely to have any direct impact on the government or on Olmert, who is under investigation over alleged corruption.
The Knesset elected Katsav as president in 2000, after Ezer Weizman, the previous president, resigned from the post after revelations that he had received $450,000 in gifts from a French millionaire.