The Kenyan parliament has passed a controversial amendment to the country’s election laws, ruling if one candidate withdraws from a repeat presidential vote the other candidate would win automatically.

The move has been heavily criticised by the country's opposition group, which boycotted the vote on the amendment.

It has also sparked unrest on the streets of the capital Nairobi, with reports of Kenyan police firing tear gas to disperse opposition protesters demanding election reforms.

It comes after opposition leader Raila Odinga, of the National Super Alliance (NASA), withdrew from a re-run of the presidential election, which is due to take place on 26 October.

He cited concerns over fairness and transparency of the upcoming vote as he pulled out of the race on Tuesday.

Kenyan opposition leader Raila Odinga, the presidential candidate of the National Super Alliance (NASA) coalition, listens as his campaign team manager Musalia Mudavadi addresses a news conference in Nairobi, Kenya August 10, 2017. 

Opposition leader Raila Odinga pulled out of the race on Tuesday

The politician renewed calls for a new electoral board to replace the Independent Electoral and Boundaries Commission (IEBC).

The new legislation must now be signed by President Uhuru Kenyatta, who may still have a challenger in the election re-run - Ekuru Aukot, who polled less than 1% the first time around.

The amendment comes as Kenya's High Court ruled that the candidate in August's presidential election could contest this month's re-run, adding to the political crisis unfolding in the country.

President Uhuru Kenyatta's initial election win was annulled by the Supreme Court

The court ruled in favour of Mr Aukot, who said he had doubts about standing while opposition activists gathered to rally for electoral reform.

He told reporters outside the High Court he still had concerns about the electoral board and would issue a statement in the following days to give clarity about his plans.

The repeat election comes after the Supreme Court annulled the original ballot, in which the incumbent Kenyan leader was declared the winner.

The court wrote off the result citing procedural irregularities.

Incumbent President Uhuru Kenyatta speaks after he was announced winner of the presidential election at the IEBC National Tallying centre at the Bomas of Kenya, in Nairobi, Kenya August 11, 2017. 

President Uhuru Kenyatta's initial election win was annulled by the Supreme Court
During the hearing, Justice John Mativo said he could "find nothing to bar the petitioner (Aukot) from contesting the fresh election".

However, it was unclear if other minor candidates from the first ballot would also seek to be included, but the election board said it had sufficient time to print ballot papers.

After pulling out of the election re-run, Mr Odinga told a news conference: "In the interest of the people of Kenya, the region and world at large, we believe that all will be best served by NASA vacating the presidential candidature of elections slated for 26 October 2017."