Kenya's opposition leader Raila Odinga has said his political alliance will be transformed into a "resistance movement", as he  called on supporters to boycott a presidential election rerun scheduled for Thursday.

Odinga made the remarks on Wednesday during a speech in Nairobi's Uhuru Park, just hours after the country's electoral commission said the vote would go ahead.

"Do not participate in any way in the sham election. Convince your friends, neighbours and everyone else to not participate," he told supporters in the Kenyan capital.

"We advice Kenyans who value democracy and justice to hold vigilance prayers or stay at home," added Odinga, leader of the National Super Alliance (NASA) coalition.

Reiterating that he will not take part in the poll, Odinga said his opposition alliance would now be transformed into a resistance movement against the government.

Deepening crisis

Kenya is holding the election re-run after the country's Supreme Court annulled the results of an August 8 poll, following a challenge by Odinga, due to "irregularities" and "illegalities" in the electoral process.

President Uhuru Kenyatta had been declared the winner of that vote.

Odinga pulled out of the new race earlier this month after claiming opposition demands to overhaul the country's election body had not been met.

Earlier on Wednesday, a last-minute attempt to block the vote failed at the Supreme Court, which was unable to raise a quorum of judges to decide on whether the poll should go ahead.

The petition was brought by three human rights activists who claimed the electoral commission is not ready to hold a credible poll.