The political crisis in Kenya appears to be deepening, with the head of the election board saying it cannot guarantee next week's presidential election rerun will be free, fair and credible.

The Independent Electoral and Boundaries Commission (IEBC) has invited the country's political leaders to meet in advance of next week's vote, which President Uhuru Kenyatta insists will go ahead.

Wafula Chebukati, the IEBC chairman, has also asked all parties to stop interfering in the election process.

Kenya is scheduled to hold a presidential election rerun next week after the country's Supreme Court annulled the results of the August 8 vote because of "irregularities" and "illegalities" in the electoral process.

In that election, more than 15 million people cast their ballots, eventually leading to a victory for Kenyatta, who secured 54 percent.

Chebukati's comments came as rallies were held in the capital Nairobi on Wednesday by the two main political parties.

The opposition has demanded that some electoral officials in charge of the last poll should be replaced.

Mass protest call

Raila Odinga, the opposition leader, called for mass protests on October 26, the day of the presidential election, which he has refused to take part in.

"Protests will go on. On the 26th [it] will be the biggest demonstrations in the whole country," he told a rally of thousands of supporters in a suburb of Nairobi.

Odinga received almost 45 percent of the vote in the August 8 election.

Kenya has witnessed weeks of street protests leading to the deaths of several opposition supporters.

A court lifted on Tuesday the government's ban on protests at major centres in the country's three main cities.

Odinga, Kenyatta's main challenger, announced last week he was pulling out of the race after claiming his demands for reform of the IEBC had not been met.

Making the announcement, he said, "All indications are that the election scheduled for 26 October will be worse than the previous one."

Commissioner resigns

In a related development, Roselyn Akombe, an election commissioner, has resigned and left Kenya, saying her staff was facing intimidation and threats.

Akombe said late on Tuesday the IEBC was "partisan" and part of the political crisis facing the country.

"It has become increasingly difficult to continue attending plenary meetings where commissioners come ready to vote along partisan lines and not to discuss the merit of issues before them," Akombe said in a statement.

"The commission in its current state can surely not guarantee a credible election on 26 October 2017. I do not want to be party to such a mockery to electoral integrity."

Local news media reported that Akombe fled to New York City, fearing for her safety.

Parliament last week passed an election law amendment stating if one candidate withdrew from the rerun vote, the remaining one would automatically win.

The vote was boycotted by opposition politicians.